Daily injection of the β2 adrenergic agonist clenbuterol improved poor muscle growth and body composition in lambs following heat stress-induced intrauterine growth restriction

Background: Intrauterine growth restriction (IUGR) is associated with reduced β2 adrenergic sensitivity, which contributes to poor postnatal muscle growth. The objective of this study was to determine if stimulating β2 adrenergic activity postnatal would rescue deficits in muscle growth, body composition, and indicators of metabolic homeostasis in IUGR offspring. Methods: Time-mated ewes were housed at 40°C from day 40 to 95 of gestation to produce IUGR lambs. From birth, IUGR lambs received daily IM injections of 0.8 μg/kg clenbuterol HCl (IUGR+CLEN; n = 11) or saline placebo (IUGR; n = 12). Placebo-injected controls (n = 13) were born to pair-fed thermoneutral ewes. Biometrics were assessed weekly and body composition was estimated by ultrasound and bioelectrical impedance analysis (BIA). Lambs were necropsied at 60 days of age. Results: Bodyweights were lighter (p ≤ 0.05) for IUGR and IUGR+CLEN lambs than for controls at birth, day 30, and day 60. Average daily gain was less (p ≤ 0.05) for IUGR lambs than controls and was intermediate for IUGR+CLEN lambs. At day 58, BIA-estimated whole-body fat-free mass and ultrasound-estimated loin eye area were less (p ≤ 0.05) for IUGR but not IUGR+CLEN lambs than for controls. At necropsy, loin eye area and flexor digitorum superficialis muscles were smaller (p ≤ 0.05) for IUGR but not IUGR+CLEN lambs than for controls. Longissimus dorsi protein content was less (p ≤ 0.05) and fat-to-protein ratio was greater (p ≤ 0.05) for IUGR but not IUGR+CLEN lambs than for controls. Semitendinosus from IUGR lambs had less (p ≤ 0.05) β2 adrenoreceptor content, fewer (p ≤ 0.05) proliferating myoblasts, tended to have fewer (p = 0.08) differentiated myoblasts, and had smaller (p ≤ 0.05) muscle fibers than controls. Proliferating myoblasts and fiber size were recovered (p ≤ 0.05) in IUGR+CLEN lambs compared to IUGR lambs, but β2 adrenoreceptor content and differentiated myoblasts were not recovered. Semitendinosus lipid droplets were smaller (p ≤ 0.05) in size for IUGR lambs than for controls and were further reduced (p ≤ 0.05) in size for IUGR+CLEN lambs. Conclusion: These findings show that clenbuterol improved IUGR deficits in muscle growth and some metabolic parameters even without recovering the deficit in β2 adrenoreceptor content. We conclude that IUGR muscle remained responsive to β2 adrenergic stimulation postnatal, which may be a strategic target for improving muscle growth and body composition in IUGR-born offspring.

Intermittent maternofetal oxygenation during late gestation improved birthweight, neonatal growth, body symmetry, and muscle metabolism in intrauterine growth-restricted lambs

In humans and animals, intrauterine growth restriction (IUGR) results from fetal programming responses to poor intrauterine conditions. Chronic fetal hypoxemia elevates circulating catecholamines, which reduces skeletal muscle β2 adrenoceptor content and contributes to growth and metabolic pathologies in IUGR-born offspring. Our objective was to determine whether intermittent maternofetal oxygenation during late gestation would improve neonatal growth and glucose metabolism in IUGR-born lambs. Pregnant ewes were housed at 40 °C from the 40th to 95th day of gestational age (dGA) to produce IUGR-born lambs (n = 9). A second group of IUGR-born lambs received prenatal O2 supplementation via maternal O2 insufflation (100% humidified O2, 10 L/min) for 8 h/d from dGA 130 to parturition (IUGR+O2, n = 10). Control lambs (n = 15) were from pair-fed thermoneutral ewes. All lambs were weaned at birth, hand-reared, and fitted with hindlimb catheters at day 25. Glucose-stimulated insulin secretion (GSIS) and hindlimb hyperinsulinemic-euglycemic clamp (HEC) studies were performed at days 28 and 29, respectively. At day 30, lambs were euthanized and ex vivo HEC studies were performed on isolated muscle. Without maternofetal oxygenation, IUGR lambs were 40% lighter (P < 0.05) at birth and maintained slower (P < 0.05) growth rates throughout the neonatal period compared with controls. At 30 d of age, IUGR lambs had lighter (P < 0.05) hindlimbs and flexor digitorum superficialis (FDS) muscles. IUGR+O2 lambs exhibited improved (P < 0.05) birthweight, neonatal growth, hindlimb mass, and FDS mass compared with IUGR lambs. Hindlimb insulin-stimulated glucose utilization and oxidation rates were reduced (P < 0.05) in IUGR but not IUGR+O2 lambs. Ex vivo glucose oxidation rates were less (P < 0.05) in muscle from IUGR but not IUGR+O2 lambs. Surprisingly, β2 adrenoceptor content and insulin responsiveness were reduced (P < 0.05) in muscle from IUGR and IUGR+O2 lambs compared with controls. In addition, GSIS was reduced (P < 0.05) in IUGR lambs and only modestly improved (P < 0.05) in IUGR+O2. Insufflation of O2 also increased (P < 0.05) acidosis and hypercapnia in dams, perhaps due to the use of 100% O2 rather than a gas mixture with a lesser O2 percentage. Nevertheless, these findings show that intermittent maternofetal oxygenation during late gestation improved postnatal growth and metabolic outcomes in IUGR lambs without improving muscle β2 adrenoceptor content.

Effect of protein and glucogenic precursor supplementation on forage digestibility, serum metabolites, energy utilization, and rumen parameters in sheep

Supplementation of glucogenic precursors in roughage diets may increase production responses due to improved efficiencies of nutrient utilization. Therefore, the objective of this study was to determine the effect of source of supplemental glucogenic potential (GP) on forage digestibility, serum metabolites, energy utilization, and rumen parameters of growing wethers consuming a roughage diet (8.8% crude protein, 71.4% ash-free neutral detergent fiber). Crossbred wethers (49.1 ± 4.7 kg initial BW; n = 16) were utilized in a 4 × 4 replicated Latin Square design with four periods of 21 d. Supplements were designed to supplement increasing amount of GP: 1) no supplementation (CON; 0 g), 2) 40 g of calcium propionate (CAP; 30 g of GP), 3) 70 g of blood meal + 100 g of feather meal (BF; 40 g of GP), or 4) combination of CAP and BF (COMBO; 70 g of GP). Total fecal and urine collection was conducted from days 13–17 to calculate digestibility estimates and urinary losses. An acetate tolerance test was administered on day 17 to determine the effect of GP on acetate clearance. Blood samples were collected on day 19 and were analyzed for serum concentrations of glucose, urea N (SUN), non-esterified fatty acids, and amino acids. Rumen fluid was collected on day 21 to determine supplementation effects on ruminal volatile fatty acid (VFA) and ammonia concentrations. Wethers receiving BF and COMBO supplementation had greatest (P ≤ 0.01) DM and OM total tract digestibility. Supplementation did not affect (P ≥ 0.37) NDF digestibility or digestible energy. Urinary nitrogen excretion was greatest (P = 0.02) for BF and COMBO. Circulating serum essential amino acid concentration was increased (P < 0.01) in BF and COMBO compared to CAP and CON. In addition, BF and COMBO had increased (P < 0.01) SUN concentrations compared to CAP and CON. Acetate half-life was not affected (P = 0.39) by supplementation strategy. However, area under the curve (AUC) for acetate was decreased (P = 0.04) with supplementation of BF and COMBO compared to CON-fed wethers. Ruminal propionate concentration was increased (P ≤ 0.01) for wethers fed CAP and COMBO supplementation, which resulted in decreased (P ≤ 0.01) A:P ratio. Overall, these results indicate that the increased propionate supply by providing propionate salts did not result in a protein sparing impact or increased N retention.

Maternofetal inflammation induced for 2 wk in late gestation reduced birth weight and impaired neonatal growth and skeletal muscle glucose metabolism in lambs

Intrauterine stress impairs growth and metabolism in the fetus and offspring. We recently found that sustained maternofetal inflammation resulted in intrauterine growth-restricted (MI-IUGR) fetuses with asymmetric body composition, impaired muscle glucose metabolism, and β-cell dysfunction near term. These fetuses also exhibited heightened inflammatory tone, which we postulated was a fetal programming mechanism for the IUGR phenotype. Thus, the objective of this study was to determine whether poor growth and metabolism persisted in MI-IUGR lambs after birth. Polypay ewes received serial lipopolysaccharide or saline injections in the first 2 wk of the third trimester of pregnancy to produce MI-IUGR (n = 13) and control (n = 12) lambs, respectively. Lambs were catheterized at 25 d of age. β-Cell function was assessed at 29 d, hindlimb glucose metabolism at 30 d, and daily blood parameters from day 26 to 31. Glucose metabolism was also assessed in flexor digitorum superficialis (FDS) muscle isolated at necropsy on day 31. Asymmetric body composition persisted in MI-IUGR neonates, as these lambs were lighter (P < 0.05) than controls at birth and 31 d, but body and cannon bone lengths did not differ at either age. FDS muscles from MI-IUGR lambs were smaller (P < 0.05) and exhibited reduced (P < 0.05) glucose oxidation and Akt phosphorylation but similar glucose uptake compared with controls when incubated in basal or insulin-spiked media. Similarly, hindlimb glucose oxidation was reduced (P < 0.05) in MI-IUGR lambs under basal and hyperinsulinemic conditions, but hindlimb glucose utilization did not differ from controls. Circulating urea nitrogen and cholesterol were reduced (P < 0.05), and triglycerides, high-density lipoprotein cholesterol, and glucose-to-insulin ratios were increased (P < 0.05) in MI-IUGR lambs. Glucose and insulin concentrations did not differ between groups during basal or hyperglycemic conditions. Although circulating monocyte and granulocyte concentrations were greater (P < 0.05) in MI-IUGR lambs, plasma tumor necrosis factor α (TNFα) was reduced (P < 0.05). FDS muscle contained greater (P < 0.05) TNF receptor 1 (TNFR1) and IκBα protein content. These findings indicate that maternofetal inflammation in late pregnancy results in fetal programming that impairs growth capacity, muscle glucose oxidation, and lipid homeostasis in offspring. Inflammatory indicators measured in this study appear to reflect heightened cytokine sensitivity in muscle and compensatory systemic responses to it.

PSI-29 Effects of maternal supplementation of ruminally undegradable protein during early gestation on subsequent progeny performance in beef cattle

Late gestation protein supplementation has been shown to be beneficial to fetal development. However, little is known about early gestation protein supplementation when supplements contain high or low amounts of ruminally undegraded protein (RUP). Therefore, two-year study was conducted using 28 mixed-aged cows consumed a basal diet balanced to meet nutrient requirements for early gestation were randomly assigned to receive one of three treatments during the first trimester of pregnancy, 1) no supplement (CON; n = 10); 2) 38% CP supplement containing 36% RUP (LRUP; n = 9); 3) 38% protein supplemented containing 50% RUP (HRUP; n = 9). All cows were managed similarly after the completion of the supplementation period. There were no treatment × year interactions observed for any variable measured. Subsequent progeny birth BW did not differ between treatments (P = 0.19). Calf weights did not differ due to treatment due to treatment (P ≥ 0.08) at weaning; however, calf weaning weight was greater in year 1 compared to year 2 (P &lt; 0.0001). After weaning, calves were placed in an individual feeding system for a 60 d feeding period. Body weight was recorded biweekly and intake was measured daily. Intake from day 0 to 14 and 14 to 28 tended to be greater (P ≤ 0.07) for HRUP and LRUP when compared to unsupplemented control. Nonetheless, ADG and gain:feed was similar for all treatments (P ≥ 0.21). Steers were transitioned to a finishing diet and harvested at approximately 18 mo of age. No differences were observed in ribeye area, hot carcass weight or yield grade (P ≥ 0.23). Overall, under the conditions of this study, supplementing cows during the first trimester with a high protein supplement that varied in ruminally undegradable protein did not impact progeny growth or carcass characteristics.

256 Heat stress and β-adrenergic agonists alter the adipose transcriptome and fatty acid mobilization in ruminant livestock

Heat stress (HS) negatively impacts livestock performance and carcass traits while beta-adrenergic agonist (βAA) supplementation improves animal production and efficiency; both can stimulate lipolysis in adipose. The objective of this study was to understand the independent and interacting effects of HS and βAA on the subcutaneous adipose transcriptome in lambs and on visceral adipose fatty acid mobilization in steers. For study 1, 24 wethers were assigned to thermal neutral (TN THI = 65) or HS (THI = 80) conditions and supplemented without (NS) or with ractopamine hydrochloride (RH) for 30d in a 2 x 2 factorial. TN lambs were pair-fed the average intake of HS. RNA collected from subcutaneous fat at harvest was sequenced. Differential expression (DE) analyses identified 71 (Padj &lt; 0.05) loci altered due to the interaction of environment and supplement. No DE genes were observed for the main effect of supplement, but HS reduced expression (P &lt; 0.05) of RBM3 and increased expression (P &lt; 0.05) of ATXN7L1. HS was predicted by pathway analyses to impair adipogenesis and fatty acid mobilization. In study 2, 24 steers were assigned to TN (THI = 65) or HS (THI = 83) and NS or zilpaterol hydrochloride (ZH) treatments for 21d in a 2 x 2 factorial. TN steers were pair-fed the intake of their HS cohort. Ex vivo fatty acid mobilization from visceral adipose in response to 0 or 1µM epinephrine was quantified at harvest. Fatty acid mobilization did not differ among groups when unstimulated, but epinephrine-stimulated mobilization was less (P = 0.05) in HS and greater (P &lt; 0.01) in ZH steers. These findings indicate that heat stress-induced reduction of fatty acid mobilization from adipose may be associated with increased expression of stress-responsive genes. Moreover, the stimulatory effect of ZH on epinephrine-induced fatty acid mobilization was present after chronic treatment. Our data have yet to identify an interaction between HS and βAA supplementation that demonstrably impacts well-being.

258 Deficits in growth, muscle mass, and body composition following intrauterine growth restriction persisted in lambs at 60 d of age but were improved by daily clenbuterol supplementation

Intrauterine growth restriction (IUGR) reduces neonatal muscle growth and alters body composition in livestock. Our objective was to determine the effect of IUGR on juvenile growth and assess the benefits of treatment with clenbuterol (β2 adrenergic agonist) in IUGR offspring. Heat stress-induced IUGR lambs were born 28% lighter (P &lt; 0.05) than controls. At 60 d of age, unsupplemented IUGR lambs had reduced (P &lt; 0.05) bodyweight (BW), average daily gain, and crown-rump length compared to controls, but clenbuterol-supplemented IUGR lambs did not differ from controls. Crown circumference, body girth, and cannon bone length did not differ among groups. Bioelectrical impedance in live lambs and carcasses estimated that lean mass and mass of multiple muscle groups were reduced (P &lt; 0.05) in unsupplemented IUGR lambs but not clenbuterol-supplemented IUGR lambs compared to controls. Estimated protein, fat, and protein/fat were likewise reduced (P &lt; 0.05) in unsupplemented but not clenbuterol-supplemented IUGR lambs. Loin-eye area in chilled carcasses was 30% smaller (P &lt; 0.05) in unsupplemented IUGR lambs but 19% larger (P &lt; 0.05) in clenbuterol-supplemented IUGR lambs compared to controls. Proximate analysis revealed greater (P &lt; 0.05) fat and reduced (P &lt; 0.05) protein and protein/fat in loin muscles from unsupplemented but not clenbuterol-supplemented IUGR lambs compared to controls. At necropsy, hindlimbs, hearts, and flexor digitorum superficialis muscles tended to be lighter (P ≤ 0.09) and lungs and kidneys were lighter (P &lt; 0.05) in IUGR lambs. Kidney weight was further reduced (P &lt; 0.05) in clenbuterol-supplemented IUGR lambs. Brain/BW tended to be reduced (P ≤ 0.09) and lung/BW and kidney/BW were reduced (P &lt; 0.05) in IUGR lambs, but lung weight and lung/BW were greater (P &lt; 0.05) in clenbuterol-supplemented compared to unsupplemented IUGR lambs. We conclude that poor growth and asymmetric body composition previously observed in IUGR neonates persists in juveniles, but daily treatment with clenbuterol recovered growth and improved body composition in IUGR lambs.

PSI-27 Effect of antral follicle count on time intervals to estrus and ovulation in crossbred beef heifers

While genetics are an unreliable indicator of fertility, antral follicle count (AFC) has recently been recognized as a useful fertility prediction tool in heifers. The aim of this study was to determine if AFC exerts an effect on response to synchronization, time to estrus (TTE), and/or time to ovulation (TTO). Twenty-five crossbred heifers were classified by AFC, either high (&gt; 25 antral follicles), moderate (16–24 antral follicles), or low (&lt; 15 follicles) and utilized in two experiments. In experiment 1, heifers were subjected to the Select Synch + CIDR fixed time artificial insemination (FTAI) protocol. After synchronization, estrus activity was monitored every 3 h until standing estrus was observed. Heifers were examined at 12 and 18 h after observation of standing estrus and every 3 h thereafter to monitor ovulation. In experiment 1, the proportion of heifers that responded to the protocol was not significant (P = 0.71) among classification groups. Time to estrus and time to ovulation were similar between groups (P &gt; 0.90). In experiment 2, heifers were placed with bulls for 60 d and were monitored for signs of estrus every 3 h. Results of experiment 2 indicated that response to estrus synchronization was similar across groups (P = 0.46). Time to estrus was greater (P = 0.04) in the high AFC group than in the low or moderate AFC groups. This may be attributed to lower concentrations of circulating gonadotropins in high AFC heifers, resulting in decreased intrafollicular estradiol. Differences in TTE results between experiment 1 and experiment 2 may be explained by increased reproductive function as heifers continued to mature during the study. These results suggest that differences in TTE may be related to AFC. Additional research is needed to corroborate these results and inform the creation of differing FTAI protocols based on AFC.

Brangus cows have ovarian reserve parameters more like Brahman than Angus cows

Bos indicus females have more surface antral follicles than Bos taurus females; however, histological studies demonstrated no difference in total number of primordial follicles between these two biological types of cattle. Primordial follicle density in the ovary was less in Nelore ovaries compared to Angus ovaries, but no studies have examined the primordial follicle density in Bos indicus cross-bred females. It, therefore, was hypothesized that primordial follicle density in the ovary would decrease as percentage Bos indicus increased. Ovaries were collected from cross-bred Angus (n = 32, no Bos indicus influence), Brangus (n = 15), or Brahman (n = 9) cows and prepared for histological evaluation. There was no difference in total number of primordial follicles per ovary between breeds (P > 0.10). When numbers of primordial follicles were expressed on a per gram of ovarian tissue basis, there were fewer primordial follicles per gram of ovarian tissue in Brangus and Brahman cows than in Angus cows (P < 0.05). Brangus cows did not differ from Brahman cows in primordial follicle density (P > 0.10). Differences in primordial follicle density could indicate differences in capacity of ovarian stroma to produce factors necessary for oogonial proliferation and primordial follicle formation among breeds. Identifying these factors could improve the aprroach for culturing pre-antral follicles of cattle. Furthermore, these results explain why ultrasonographic antral follicle counts may need to be adjusted to a greater threshold to predict size of the ovarian reserve and determine ovarian reserve related reproductive traits in Bos indicus females.

Evaluation of estrous synchronization protocols on ewe reproductive efficiency and profitability

A 2-year experiment was conducted to determine the effect of a single injection of prostaglandin after initiation of the breeding season on ewe estrous synchronization. Rambouillet ewes (n = 101; Year 1 = 52; Year 2 = 49) assigned to one of three treatments: untreated (CON); 12-d CIDR insert (CIDR); or 1 injection of prostaglandin at d 2.5 (1 PG) after rams were placed with ewes. Rams were placed with ewes at the time of CIDR removal (d 0) and remained with ewes during a 35-d breeding season. Both the CIDR- (94%) and 1 PG (73.5%) treatment groups had a larger number (P ≤ 0.01) of ewes bred in the first 5 d of the breeding season compared to ewes of the control (33%) group. As expected, CIDR-treated ewes had a shorter time to mating, than 1 PG-treated ewes and ewes of the control group had a longer interval to mating than both CIDR- and 1 PG-treated ewes (P ≤ 0.01). The number of lambs born per ewe and kg of lamb weaned per ewe was not different (P ≥ 0.31) among treatment groups. Additionally, there was no difference (P =  0.78) in net profit per ewe among treatment groups. Based on these data, utilizing a single injection of PG 2.5 d after initiation of the breeding season resulted in similar pregnancy rates at d 5 of the breeding season when compared with CIDR-treated ewes indicating the potential utilization of the 1PG protocol in a confinement setting as a viable method for estrous synchronization.

The effect of cow udder score on cow/calf performance in the Nebraska Sandhills

Poor udder and teat confirmation decreases profitability due to decreased calf weaning weight, increased incidence of mastitis and labor, and decreased cow lifetime productivity. Therefore, the objective of this retrospective study was to evaluate the effect of beef cow udder score on cow performance and pre- and postweaning progeny performance. In a 5-yr study, crossbred cows at the Gudmundsen Sandhills Laboratory, Whitman, NE, were assigned an udder score each year at calving, from 1 to 5, using an udder and teat combination score. Cows were grouped by udder scores and classified as either low udder score (LUS, udder score 1 or 2; n = 223) or high udder score (HUS, udder score 3 or 4; n = 1,742). The udder score combines udder conformation and a teat scoring system. Low udder scores consisted of pendulous udders and large teats, whereas HUS consisted of tight udders and small, symmetrical teats. Mixed models were used to evaluate udder score on cow performance and calf pre- and postweaning performance. Cow body weight (BW) at prebreeding and weaning was greater (P < 0.01) in LUS cows compared with HUS counterparts. Pregnancy rate was not different (P = 0.35) between udder classification groups. Calf BW at birth (P = 0.95), weaning (P = 0.40), and adjusted 205-d BW (P = 0.28) were not different between udder groups. Cow udder score did not influence feedlot entry (P = 0.41) and final BW (P = 0.30), dry matter intake (P = 0.53), average daily gain (P = 0.60), and gain:feed ratio (P = 0.85) of steer progeny. However, steers from HUS dams had greater hot carcass weight (HCW; P = 0.04) and backfat thickness (P = 0.02) compared with LUS counterparts. Results from this study suggest cows with less desirable udder structure may not have a negative impact on calf preweaning growth and performance; however, backfat thickness and HCW in the finishing phase were lower in steers from cows with a lower udder score.

BEEF SPECIES-RUMINANT NUTRITION CACTUS BEEF SYMPOSIUM: Sustainable and economically viable management options for cow/calf production through enhanced beef cow metabolic efficiency1

Beef cow herds are expected to be metabolically and reproductively efficient in varied and ever changing environmental conditions. Therefore, selection and management of grazing beef cows provides unique and diverse challenges in achieving optimal production efficiency for any environment. Beef cows face dynamic and highly variable nutritional environments that periodically are inadequate in meeting nutrient and energy requirements. Nutritional management during high metabolically stressed and key physiological states can lead to increased or decreased metabolic efficiency. Conversely, cow metabolic efficiency may be reduced in many production systems due to surplus nutritional inputs and reduced exposure to environmental stressors. Alternatively, metabolically potent supplementation strategies targeting enhanced energy metabolism and endocrine mechanisms would increase beef cow metabolic and economic efficiency. Metabolic efficient beef cows adapt to environmental changes by adjusting their metabolic energy utilization in order to match current environmental conditions and remain reproductively competent. This mechanism involves adaptive processes that drive adjustments in nutrient partitioning and energy utilization efficiency. However, the variation in metabolic and reproductive efficiency among beef cows within cow/calf production systems is substantial, suggesting a lack of complete integration of nutrition, genetics, and reproduction with environmental constraints and conditions. Better integration and understanding of the interactions may lead to advancements in metabolic efficiency of the cowherd. Metabolic flexibility is recognized as an important trait in dairy production but has received little attention thus far in beef cattle. Overall, management and supplementation strategies in cow/calf systems from a mechanistic, targeted nutritional approach during key physiological periods would hasten improvements in metabolic efficiency.

The effect of precipitation received during gestation on progeny performance in Bos indicus influenced beef cattle

The objective of this retrospective study was to determine the effect of precipitation level during key fetal development periods on beef progeny performance. The hypothesis that was precipitation level during different periods of gestation would program subsequent calves for an environment similar to that experienced in utero resulting in altered growth and reproductive performance. Data were collected on Brangus cows (n = 2,429) over a 46-yr span at the Chihuahuan Desert Rangeland Research Center. Recorded precipitation values were used to calculate average precipitation associated with total gestation (April–March), early gestation, (July–September), and late gestation (December–February). These values were used to classify treatments: low (z value ≤ –1.00), average (z value –0.99 to +0.99), and high (z value ≥ +1.00) for each time period. Calves experiencing high precipitation throughout gestation had heavier body weight (BW) at birth (P = 0.02), weaning (P = 0.05), and adjusted 205-d BW (P = 0.04) than those experiencing low precipitation . Female progeny gestated during low precipitation throughout gestation were more likely to remain (P < 0.0001) in the herd and calve after the age of 8 yr when compared to heifers experiencing high precipitation levels in utero (38% vs. 16% ± 5%, respectively). In addition, a greater percentage (P < 0.0001) of heifers experiencing low precipitation levels during the early gestation period produced a calf within the herd after 8 yr of age. Similarly, calves experiencing low precipitation during those same time points also had a greater number of calves while in production (P < 0.0001) when compared to the average and high precipitation groups. These results indicate that selection of heifers exposed to lower than average precipitation levels in utero may result in increased herd retention and productivity.

Bacterial endospore inactivation caused by outgassing of vapourous hydrogen peroxide from polymethyl methacrylate (Plexiglas)

AIMS

To investigate the cause and to eliminate the inactivation of Bacillus anthracis strain Sterne spores settled onto agar and stainless steel surfaces in plastic holders.

METHODS AND RESULTS

In an experimental chamber in which spores settled onto sampling surfaces, vapourous hydrogen peroxide (VHP) was used for decontamination between experiments. It was demonstrated that hydrogen peroxide (H(2)O(2)) absorbed into plastic (Plexiglas) surfaces and could outgas in the sample holders. Further experiments demonstrated that H(2)O(2) was released from Plexiglas sample holders in sufficient quantity to inactivate spores. High temperature degassing (30-35 degrees C) for several days or aluminum coating of the surfaces were two remedies found to be effective in preventing inadvertent spore inactivation.

CONCLUSIONS

H(2)O(2) can be absorbed into plastic and released after an extended period of time (weeks), allowing a sufficient concentration to accumulate in small volumes to inactivate spores. Outgassing the plastic or coating the surface with an impermeable layer are potential solutions to reduce spore inactivation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Many studies with bacilli and other organisms are carried out using small plastic containers that may have been sterilized using H(2)O(2) or other agents. This study presents a cautionary note to ensure elimination of H(2)O(2) or other sterilizing agents to prevent spurious results.