The effects of accelerated growth rates and estrogen implants in prepubertal Holstein heifers on growth, feed efficiency, and blood parameters

Effect of estradiol and predator cues on behavior and brain responses of captive female house sparrows (Passer domesticus)

The presence of predators can cause major changes in animal behavior, but how this interacts with hormonal state and brain activity is poorly understood. We gave female house sparrows (Passer domesticus) in post-molt condition an estradiol (n = 17) or empty implant (n = 16) for 1 week. Four weeks after implant removal, a time when female sparrows show large differences in neuronal activity to conspecific vs. heterospecific song, we exposed birds to either 30 min of conspecific song or predator calls, and video recorded their behavior. Females were then euthanized, and we examined neuronal activity using the expression of the immediate early gene (IEG) ZENK to identify how the acoustic stimuli affected neuronal activation. We predicted that if female sparrows with estradiol implants reduce neuronal activity in response to predator calls as they do to neutral tones and non-predatory heterospecifics, they would show less fear behavior and a decreased ZENK response in brain regions involved in auditory (e.g., caudomedial mesopallium) and threat perception functions (e.g., medial ventral arcopallium) compared to controls. Conversely, we predicted that if females maintain auditory and/or brain sensitivity towards predator calls, then female sparrows exposed to estradiol would not show any differences in ZENK response regardless of playback type. We found that female sparrows were less active during predator playbacks independent of hormone treatment and spent more time feeding during conspecific playback if they had previously been exposed to estradiol. We observed no effect of hormone or sound treatment on ZENK response in any region of interest. Our results suggest that female songbirds maintain vigilance towards predators even when in breeding condition.

Highly sensitive determination of endocrine disrupting chemicals in foodstuffs through magnetic solid-phase extraction followed by high-performance liquid chromatography-tandem mass spectrometry

BACKGROUND

Endocrine disrupting chemicals (EDCs), proved to be potential carcinogenic threats to human health, have received great concerns in food field. It was essential to develop effective methods to detect EDCs in food samples. The present study proposed an efficient method to determine trace EDCs including estrone (E1), 17β-estradiol (E2), estriol (E3) and bisphenol A (BPA) based on magnetic solid-phase extraction (MSPE) coupled high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) in meat samples.

RESULTS

Fe₃ O₄ @COF(TpBD)/TiO₂ nanocomposites were synthesized via functionalization of magnetic covalent organic frameworks (COFs) with titanium dioxide (TiO₂ ) nanoparticles, and used as absorbents of MSPE to enrich EDCs. The efficient EDCs enrichment relies on π-π stacking interaction, hydrogen bonding, and the interaction between titanium ions (IV, Ti⁴⁺ ) and hydroxyl groups in EDCs, which improves the selectivity and sensitivity. Under the optimized conditions, target EDCs were rapidly extracted through MSPE with 5 min. Combining Fe₃ O₄ @COF(TpBD)/TiO₂ based MSPE and HPLC-MS/MS to determine EDCs, good linearities were observed with correlation coefficient (R² ) ≥ 0.9989. The limits of detection (LODs) and limits of quantification (LOQs) were 0.13-0.41 μg kg^-1 and 0.66-1.49 μg kg^-1 , respectively. Moreover, the proposed method was successfully applied to real samples analysis.

CONCLUSIONS

The established MSPE-HPLC-MS/MS method was successfully applied to determine EDCs in meat samples with rapidness, improved selectivity and sensitivity. It shows great prospects for EDCs detection in other complicated matrices. © 2020 Society of Chemical Industry.

Polymorphism of insulin-like growth factor 1 gene and its relationship with reproductive performances and milk yield in Sarda dairy sheep

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IGF-1 gene plays an important role in regulating reproduction in ruminants.

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Here three SNPs were found in the IGF-I gene in Sarda sheep.

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The found SNPs were related to reproductive performance and milk yield.

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This results could be used to improve the reproductive performances and milk yield in Sarda sheep.

The aim of this research was to detect polymorphisms within the IGF-I gene in dairy sheep and to verify their influence on milk yield and reproductive performances. Four hundred Sarda ewes in their second lactation were selected from 2 farms. Their reproductive traits (fertility rate, interval in days from ram introduction to lambing and litter size) and milk yield were recorded, from the second to the fourth lactation. DNA was extracted from individual blood samples and subjected to amplification and sequencing of the IGF-I gene 5′ UTR and Exon 3 regions. Three polymorphic sites were recorded at positions g184028491C>G and g184028489C>T of the 5′UTR, and g184023223G>A of the Exon 3. The C allele at position g184028491 showed a significant association with higher fertility rate (P < 0.05) and a shorter interval in days from ram introduction to lambing (P < 0.01). In addition, a significant effect of the CC genotype was found with higher milk yield for P < 0.05 in the second and third lactation, and P < 0.01 in the fourth lactation compared to the other genotypes. Even, AA genotype at position g184023223 of the exon 3 showed a positive significant effect on milk yield for P < 0.05, in the second and third lactation, and for P < 0.01 in fourth lactation compared to the other genotypes. In conclusion the found SNPs showed a significant influence on reproductive performances and milk yield in Sarda sheep breed suggesting a possible application in sheep selection plans.

The impact of early life nutrition and housing on growth and reproduction in dairy cattle

Contentious issues in calf rearing include milk feeding practices and single versus group housing. The current study was performed on a high producing 170 Holstein cow dairy farm, to investigate the impact of nutrition and housing on growth and reproduction. Heifer calves (n = 100) were allocated in birth order to one of two commonly used management strategies. All calves received 3-4 litres of dam specific colostrum within 6 hours of birth. Group A calves were group housed from birth and fed milk replacer (MR) ad libitum via a computerised machine utilising a single teat, with weaning commencing at 63 days of age. Group R calves were initially housed in individual pens and received 2.5 litres of MR twice daily via a bucket until 21 days of age when they were group housed and fed 3 litres of MR twice daily via a group trough with weaning commencing at 56 days. From 12 weeks of age onwards, calves in both dietary groups were subject to common nutritional and husbandry protocols. All breeding of heifers was via artificial insemination with no hormonal intervention. Calves were weighed, body condition scored and morphometric measures recorded weekly up till 12 weeks of age then monthly until conception. Pre-weaning growth rates (kg/day) were significantly higher in Group A calves compared to Group R (0.89, 95% CI 0.86-0.93 vs 0.57, 95% CI 0.54-0.6 kg/day P < 0.001) with the most marked differences observed during the first three weeks of life (0.72, 95% CI 0.61-0.82 vs 0.17, 95% CI 0.08-0.26 P < 0.001). Whilst Group A calves gained body condition score (BCS) throughout the pre-weaning phase, Group R calves lost BCS during the first 4 weeks of life. Data suggested that Group R calves supported skeletal growth during this period by catabolising body tissue. Group A calves had a greater risk of disease than group R calves during the pre-weaning phase (diarrhoea: odds ratio 3.86, 95% CI 1.67-8.9; pneumonia: odds ratio 5.80, 95% CI 2.33-14.44) although no calves died during this period. Whilst pneumonia had a significant impact on growth during the study duration (P = 0.008), this was not the case for diarrhoea. Whilst univariate analysis failed to show any statistically significant group differences (P > 0.050) in any of the mean values of measured reproductive parameters, multivariable Cox regression suggested that there was a weak trend (P = 0.072) for Group A animals to achieve first service earlier than their Group R counterparts (62.6 weeks versus 65.3 weeks). Irrespective of dietary group, the hazard for achievement of all measured reproductive parameters, apart from time to puberty, was 20-40% less for heifers borne from multiparous dams compared to heifers from primiparous dams.

Effects of rearing regime on body size, reproductive performance and milk production during the first lactation in high genetic merit dairy herd replacements

One hundred and thirteen high genetic merit Holstein-Friesian heifers were used in a study to determine the effect of rearing regime, in terms of diet offered and target calving weight, on body size, reproductive performance and milk production in high genetic merit heifers. Eighty of the heifers were supplied from 11 commercial farms, the remainder were supplied from the herd at the Agricultural Research Institute of Northern Ireland. The heifers commenced the experiment at 7 weeks of age when they were allocated on the basis of source, live weight and genetic merit to one of four rearing regimes. The target weights at calving were 540 kg (treatment 1) and 620 kg (treatments 2, 3 and 4). Treatment 1 heifers were offered grass silage-based diets during the winter and grass-based diets during the summer. Treatment 2 heifers were offered the same forage base plus additional concentrate supplementation. Treatment 3 heifers were offered a straw/concentrate diet during the winter and grass-based diets during the summer. Treatment 4 heifers received the same diets as treatment 3, except for the first summer period when they remained housed and were offered a straw/concentrate diet. The heifers were mated at 14 months of age and were returned to the 11 source farms one month prior to calving. Heifers reared on treatment 1 had a lower withers height (P < 0·001) and were of a lower condition score (P < 0·001) before calving than heifers reared on treatments 2, 3 and 4. During early lactation (3 months post calving) heifers reared on treatment 1 lost less weight and condition score than the heifers reared on the other treatments. Thus at the end of the first lactation live weights did not differ significantly between the treatments. However, body length remained shorter (P < 0·01) in treatment 1 compared with treatments 2, 3 and 4. First lactation milk yield (305 days) was lower for heifers reared on treatment 1 (7222 l) compared with heifers reared on treatment 2 (8020 l) (P < 0·01), 3 (7956 l) (P < 0·01) and 4 (7901 l) (P < 0·05). Similarly, milk fat plus protein yield was lower (P < 0·05) for heifers reared on treatment 1 (511 kg) compared with treatments 2 (544 kg), 3 (544 kg) and 4 (554 kg). The interval from calving to first recorded oestrus was shorter in treatment 1 compared with treatments 2 and 3 (P < 0·05). There was a tendency (P < 0·10) for heifers reared on treatment 1 to have a shorter calving interval (394 days) compared with treatments 2 (426 days), 3 (435 days) and 4 (458 days). In conclusion increasing the live weight of Holstein-Friesian heifers at first calving from 540 to 620 kg pre-calving increased milk yield proportionally by 0·11 but tended to increase the calving interval. Diet type during the rearing period had no effect on milk fat plus protein yield or reproductive performance.

Growth targets and rearing strategies for replacement heifers in pasture-based systems: a review

Dairy heifer growth and liveweight at first calving are regarded as important management variables affecting profitability and animal welfare. However, the appropriateness of heifer growth rate targets for different farming systems is not clear. Retrospective assessments of the association between heifer liveweight and subsequent productivity indicate significant benefits in milk production and, even, reproduction from increasing liveweight at breeding and first calving. However, prospective interventionist experiments do not concur, with very variable effects of liveweight at breeding on milk production and with only limited evidence of a positive effect of first-calving liveweight on first-lactation milk yield. In addition, any benefit in the first lactation is not evident in subsequent lactations in the limited number of long-term studies reported. Pre-weaning nutrition and average daily weight gain are areas of increasing interest, with lifelong increases in milk production resulting from accelerated growth rates during the first 8 weeks of life, indicating a possible significant return from a short-term investment. This could be one reason for the inconsistent effects of heifer liveweight at breeding and first lactation on milk production. Although the effect of pre-weaning average daily gain on heifer liveweight is short-lived, a recent meta-analysis indicated that pre-weaning average daily gain explains 22% of the variation in first-lactation milk production. Whether these differences in animal physiology have relevance in grazing systems, wherein heifers and cows do not consume sufficient nutrients to reach their potential, requires investigation. Despite considerable extension efforts over successive decades, current evidence indicates that failure to provide the new-born calf with sufficient high-quality colostrum is common. To understand the reasons for suboptimal colostrum feeding requires social research, with appropriate extension strategies developed to elicit practice change. Although there can be little doubt regarding the importance of heifer rearing to the profitability and sustainability of the farming business, the collective literature points to a failure of retrospective analyses in determining the cause of poor heifer performance. In reality, it is likely to be a combination of factors. The objective of this review is to investigate the effect of liveweight gain at various stages of the growth cycle of the heifer on the milk-production capacity of the lactating animal.

Nitrogen metabolism and recycling in yaks (Bos grunniens) offered a forage - concentrate diet differing in N concentration

An experiment was conducted to characterise N use efficiency and quantify urea fluxes in yaks offered four levels of dietary N (1.43%, 1.97%, 2.45% and 2.90% of diet DM) in a 4 × 4 Latin square design. The incremental increase in N intake linearly increased N retention (P = 0.003) and the excretion of urinary N (P < 0.001), but no difference (P > 0.05) in faecal N excretion was observed in growing yaks fed any of the four diets. Microbial N production had quadratic (P < 0.001) responses to dietary N, characterised by the highest microbial N production occurring in the 1.97% N diet (P < 0.05). As the N content of the diet increased, the urinary excretion of urea increased from 13% to 27% of urea entry rate (quadratic, P < 0.001), whereas gastrointestinal entry urea returned to ornithine cycling decreased from 46% to 40% (linear, P < 0.001), and the gastrointestinal entry urea used for anabolism increased from 50% to 56% (linear, P < 0.001). Gastrointestinal entry urea incorporated into bacterial N decreased linearly (P < 0.001) with incremental increase in N intake, and the greatest concentration (23.5%) of bacterial N originating from plasma urea N was in yaks fed the 1.43% N diet. As much as 87% of the urea synthesised in the liver was returned to the gastrointestinal tract when the yaks were fed a diet with 1.43% N (1.1 times the maintenance N level). Moreover, constantly greater urea production than the intake of digestible N, and the gastrointestinal-urea clearance than the kidney-urea clearance were observed, respectively, in the growing yaks, regardless of the level of N intake. These results suggest that yaks might be more efficient at utilising N under harsh environment than are cattle.

Construction of uniformly sized pseudo template imprinted polymers coupled with HPLC-UV for the selective extraction and determination of trace estrogens in chicken tissue samples

To assess the potential risks associated with the environmental exposure of steroid estrogens, a novel highly efficient and selective estrogen enrichment procedure based on the use of molecularly imprinted polymer has been developed and evaluated. Herein, analogue of estrogens, namely 17-ethyl estradiol (EE(2)) was used as the pseudo template, to avoid the leakage of a trace amount of the target analytes. The resulting pseudo molecularly imprinted polymers (PMIPs) showed large sorption capacity, high recognition ability and fast binding kinetics for estrogens. Moreover, using these imprinted particles as dispersive solid-phase extraction (DSPE) materials, the amounts of three estrogens (E(1), E(2) and E(3)) which were detected by HPLC-UV from the chicken tissue samples were 0.28, 0.31 and 0.17 μg g(-1), and the recoveries were 72.5-78.7%, 90.3-95.2% and 80.5-83.6% in spiked chicken tissue samples with RSD <7%, respectively. All these results reveal that EE(2)-PMIPs as DSPE materials coupled with HPLC-UV could be applied to the highly selective separation and sensitive determination of trace estrogens in chicken tissue samples.

Replacement Management in Cattle | Breeding Standards and Pregnancy Management

Rearing replacement heifers is part of herd survivability and represents 15–20% of total farm costs. Proper attention to the growth of heifers is paramount to producing heifers that achieve adequate stature and body weight before first breeding and calving. Timely entry of heifers into the milking herd by 2 years of age, or their first eligible calving season in seasonal pasture-based dairy enterprises, can be facilitated by applying synchronization of estrus and ovulation in addition to traditional detection of estrus by visual or other means. Because fertility is better in heifers than in lactating cows, artificial insemination of heifers with semen from the best available progeny-tested bulls is a wise investment to ensure genetic gain of economically important traits. Annual culling rates of 25–33% necessitate a supply of herd replacement heifers. Application of gender-biased semen to produce more female offspring is also warranted for increasing the replacement population. The main goal of a heifer replacement program is to develop heifers at minimal cost and in a timely manner to obtain heifers of desired size and body weight so that they attain puberty, establish pregnancy, calve easily, and achieve their maximum genetic lifetime milk production as cows.

Biological markers of neonatal calf performance: the relationship of insulin-like growth factor-I, zinc, and copper to poor neonatal growth

Raising a heifer calf to reproductive age represents an enormous cost to the producer. Poor neonatal growth exacerbates the costs incurred for rearing, and use of blood variables that may be associated with poorly growing calves may offer predictive value for growth and performance. Thus, the principal objective of the present study was to describe changes in serum IGF-I, zinc, and copper from birth to 90 d in Holstein calves, while accounting for sex and twin status, in poorly growing calves and calves growing well. A second objective was to test the hypothesis that an association exists between these serum variables and morphometric indicators of growth. Measurements of BW, length, and height were recorded at birth and at 30, 60, and 90 d of age. Jugular blood (12 mL) was collected from each calf on d 1 to determine serum total protein, serum IgG, packed cell volume, serum zinc, serum copper, serum IGF-I, and CD18 genotype for bovine leukocyte adhesion deficiency; serum zinc, serum copper, and serum IGF-I (predictor variables) were also determined for each calf on d 2 through 10 and on d 30, 60, and 90. Stepwise multiple regression and logistic regression analyses were used to examine the relationships between the predictor variables and the dependent variables (BW, height, and length at d 30, 60, and 90 of life). Birth weight, sex, serum IGF-I (at all ages), serum copper, and the serum copper-to-zinc ratio were associated, to varying degrees, with the dependent growth variables. Birth weight was consistently the dominant predictor. In conclusion, these results suggest that lighter birth weight, reduced serum IGF-I, and inflammation may be important causes of poor growth in neonatal Holstein dairy calves.

The role of endocrine insulin-like growth factor-I (IGF-I) in female bovine reproduction

Insulin-like growth factor-I (IGF-I) plays a pivotal role in cattle fertility, acting as a monitoring signal that allows reproductive events to occur when nutritional conditions for successful reproduction are reached. However, endocrine IGF-I is not a predictor of reproductive events, but rather an indirect estimator of the suitability of the animal to achieve the reproductive event in question. Although measuring circulating IGF-I concentrations might not have any clinical application in the cattle industry, endocrine IGF-I screening will continue to be important for the study of interactions between nutrition and reproduction. In addition, endocrine IGF-I screening could be used as an ancillary test for the selection of cattle for high reproductive potential, especially in herds of high genetic merit for milk production, in which a decline in fertility has been identified.

Luteinizing hormone-releasing hormone fusion protein vaccines block estrous cycle activity in beef heifers1

Two LHRH fusion proteins, thioredoxin and ovalbumin, each containing seven LHRH inserts were tested for their ability to inhibit estrous cycle activity. The objective was to evaluate immune and biological responses from alternating the two fusion proteins in an immunization schedule. One hundred ten heifers were divided equally into 11 groups. Two control groups consisted of either spayed or intact, untreated heifers. Heifers in the other nine groups were immunized on wk 0, 4, and 9. Treatments were immunizations of the same protein throughout or alternating the proteins in different booster sequences. Blood was collected weekly for 22 wk, and serum was assayed for concentrations of progesterone and titers of anti-LHRH. At slaughter, reproductive tracts were removed from each heifer and weighed. Heifers with >or=1 ng/mL of progesterone were considered to have a functional corpus luteum and thus to have estrous cycle activity. All LHRH-immunized groups of heifers had a smaller (P < 0.05) proportion of heifers showing estrous cycle activity after 6 wk than the intact, untreated control group. There was no difference in number of heifers cycling between the immunized groups and the spayed heifers during wk 9 to 22. Anti-LHRH did not differ among immunized groups during wk 1 to 9. Starting at wk 10 and continuing through the conclusion of the study, there was an overall difference among treatment groups for anti-LHRH (P < 0.05). Uterine weights differed among treatments (P < 0.05), with intact control animals having heavier uteri than all other groups (P < 0.05). Uterine weights were negatively correlated with maximum LHRH antibody binding (r = -0.44). In summary, the LHRH fusion proteins were as effective as surgical spaying in suppression of estrous cycle activity, but alternating the two proteins in an immunization schedule did not enhance the immunological or biological effectiveness of the vaccine.

IGF-I mRNA levels in bovine satellite cell cultures: effects of fusion and anabolic steroid treatment

Androgenic and estrogenic steroids enhance muscle growth in a number of species; however, the mechanism by which anabolic steroids enhance muscle growth is not known. Castrated male cattle (steers) provide a particularly good model system in which to study the effects of anabolic steroids on muscle growth because they respond dramatically to treatment with both estrogens and androgens. The goal of this study was to determine if treatment of bovine satellite cell (BSC) cultures with 17beta-estradiol (E(2)) or trenbolone (a synthetic androgen) directly affects proliferation rate or level of mRNA for estrogen receptor (ER)-alpha, androgen receptor, and growth factors that have been shown to affect muscle growth (insulin-like growth factor (IGF)-I, IGF binding protein (IGFBP)-3, and myostatin). BSC cultures were established from the semimembranosus muscles of steers and then treated for 48 h with various concentrations of E(2) or trenbolone ranging from 0.001 to 10 nM. IGF-I mRNA levels in proliferating BSC cultures were significantly increased at 0.01 (1.9-times control values, P < 0.02) and at 0.1, 1, and 10 nM E(2) (2.9-, 3.5-, and 3.5-times control values, respectively, P < 0.0001). Additionally both 1 and 10 nM trenbolone increased IGF-I mRNA levels to 1.7-times control values (P < 0.02). ER-alpha mRNA was detectable in BSC cultures, and levels were increased (2.3-times control levels, P < 0.001) in cultures treated with 0.001 nM E(2) but not in cultures treated with higher concentrations of E(2). Androgen receptor mRNA levels also were increased (1.5-times control levels, P < 0.02) in cultures treated with 0.001 nM trenbolone but not by treatment with higher concentrations of trenbolone. Levels of IGFBP-3 were increased (1.4-times control values, P < 0.02) by treatment with 0.001 nM E(2) but not by treatment with high concentrations of E(2). Myostatin mRNA levels were not affected by any concentration of either of the steroids. Although, levels of IGF-I mRNA were 10-times greater (P < 0.02) in fused BSC cultures than in proliferating cultures, treatment of fused cultures for 48 h with 10 nM E(2) increased IGF-I mRNA levels (2.5-times control levels, P < 0.02). Both E(2) and trenbolone increased (3)H-thymidine incorporation rate (1.5-times control levels, P < 0.001) in BSC cultures in media containing serum from which IGFBP-3 had been removed by anti-IGFBP-3 affinity chromatography. In summary, treatment of BSC cultures with either E(2) or trenbolone increased IGF-I mRNA level and proliferation rate, thus, establishing that these steroids have direct anabolic effects on cells present in the BSC culture.

Nitrogen metabolism and recycling in Holstein heifers

To study the effect of dietary N level on urea kinetics and recycling, four Holstein heifers (267 +/- 3.6 kg) were used in a Youden square design. Isocaloric diets with a N content of 1.44, 1.89, 2.50, 2.97, and 3.40% were fed at approximately 1.8 times maintenance intake. Increasing the N content of the diet increased urinary N excretion (P < 0.001) and N balance (P < 0.01), but did not affect the fecal N excretion (P = 0.21). Increasing the level of dietary N, increased urea production (P < 0.001) and excretion (P < 0.001), but no effect (P = 0.24) could be detected in the amount of N recycled to the gut. Urea recycled with the saliva, however, increased (P < 0.001) both in absolute and relative terms, with increasing dietary N. No difference could be detected on the amount of recycled N that was used for anabolism or returned to the ornithine cycle, but less (P = 0.001) N originating from urea was excreted in feces as dietary N increased. Ruminal ammonia concentration increased (P < 0.001) with increasing N intake, but total tract neutral detergent fiber digestibility was depressed only on the lowest N intake diet. No difference (P = 0.30) was detected in ruminal microbial yield among diets, but more (P < 0.003) N was derived from blood urea at low N intakes, and the efficiency of use of the recycled N decreased (P < 0.001) with increasing levels of dietary N. Adaptive changes to low-N diets were a decrease (P < 0.003) in the renal clearance of urea and an increase (P < 0.001) in the gastrointestinal clearance of urea. Urea transporters were present in the rumen wall of the heifers and differentially expressed depending on dietary N content, but their role in the transfer of urea into the rumen remains uncertain. Different mechanisms of N salvage and recycling were involved when animals were fed low-N diets that ensured a supply of endogenous N to the gastrointestinal tract and, due to the reduced contribution of dietary N, an increased efficiency of the N recycled was observed.

The response of altering the ratio of dietary protein to energy on growth, feed efficiency, and mammary development in rapidly growing prepubertal heifers

This study was conducted to evaluate the effects of increasing the ratio of dietary protein to energy above National Research Council recommendations on average daily gain, feed efficiency, structural growth, and indirect measurements of mammary growth. Forty-five Holstein heifers were randomly assigned to either a low, medium, or high ratio of dietary crude protein (CP) to metabolizable energy of 46:1, 54:1, and 61:1 g/Mcal, respectively. The ratio of dietary protein to energy was altered by adjusting the concentration of CP with a similar amount of energy across all diets. Heifers were individually fed and began the treatment period at 200 kg of body weight and 28 wk of age. During the 3-wk adaptation period and 20-wk treatment period, all heifers were fed for a daily dry matter intake (DMI) of 2.45% of body weight. Body weight was monitored for two consecutive days each week and was used to adjust the dry matter offered on a weekly basis. The high versus low ratio of dietary protein to energy increased feed efficiency 6%, which resulted in larger heifers that were subsequently fed 3% more DMI over the course of the trial. The increased feed efficiency and DMI increased average daily gain by 9% for the high versus low ratio of dietary protein to energy. For the high versus low ratio of dietary protein to energy, hip width, hip height, wither height, and heart girth growth was increased 13, 16, 18, and 12%, respectively. The heifers fed the high ratio of dietary protein to energy had a lower rate of increased body condition score compared with the heifers fed the low ratio of dietary protein to energy. Teat length growth was used as an indirect measurement of mammary ductal development and was increased by 35 to 38% for heifers on the high versus low ratio of dietary protein to energy. Feeding dietary ratios of protein to energy above NRC recommendations improved feed efficiency and increased average daily gain, structural growth, and mammary development while decreasing body condition scores in heifers between 28 and 48 wk of age.

The effects of accelerated growth rates and estrogen implants in prepubertal Holstein heifers on estimates of mammary development and subsequent reproduction and milk production

The objectives of this study were to determine the effects of accelerating growth rates and of imposing estrogen implants in prepubertal heifers on mammary development and subsequent reproduction and milk production. Sixty-eight Holstein heifers were assigned to 1 of 4 treatment groups by using a randomized complete block design in a 2 x 2 factorial arrangement. The treatments were standard growth rate (700 g/d) or accelerated growth rate (1000 g/d) and estrogen implant or no estrogen implant. The treatments were imposed over 20 wk, beginning at 4.5 mo of age and 130 kg of body weight (BW). During the treatment period, all heifers were fed individually and received the same diet, but the dry matter intake of each heifer was adjusted weekly to achieve the designated growth rate. The estrogen implants were removed at the end of the treatment period at 9.5 mo of age. After the treatment period, the heifers were group fed according to BW and age to allow the heifers to have a similar BW and age at calving. The accelerated growth regimen decreased age at puberty by 32 d. Age, BW, and body condition scores at calving were not significantly different among treatments. The accelerated prepubertal growth regimen decreased first lactation fat-corrected milk yield 7.1%. Prepubertal heifers given estrogen implants produced 5.2% less fat-corrected milk during first lactation than did heifers not implanted with estrogen. Estrogen implants stimulated a large increase in teat length growth during the treatment period, but the advantage was lost posttreatment. Over both the treatment and posttreatment periods, the estrogen implants reduced teat length growth by 30%. Accelerated growth rates from 700 to 1000 g/d and estrogen implants in prepubertal heifers decreased first lactation milk production.