Reduced response to an estrous induction program in postpartum beef cows treated with zilpaterol and gaining body weight

Short-term methionine supplementation during the early post-partum period in primiparous rabbits improves prolificacy associated with an increase in serum concentrations of IGF-I

The aim of this study was to evaluate the effects of methionine supplementation on energy metabolism and reproductive performance during the early post-partum period in primiparous does. Forty nulliparous New Zealand White does were used. Females were randomized in two groups at calving: the control group (n = 20) was fed with the basal diet, and the methionine group (n = 20) was fed the basal diet plus 1 g/animal/day of methionine from the day of calving to 4 days post-partum. Results showed that methionine supplementation increased (p = 0.032) the concentration of insulin-like growth factor-1 with respect to control group 4 days post-partum. It similarly increased the prolificacy (p = 0.03), the number of kits born alive per litter (p = 0.06) and the body gain weight of the litter during supplementation (p = 0.035). These results were observed despite the does in the methionine group having a deeper negative energy balance than the does in the control group. Finally, methionine supplementation did not affect receptivity (p = 0.23), fertility (p = 0.49), the number of kits born dead per litter (p = 0.86) insulin and metabolites as glucose, non-esterified fatty acids and triglycerides. In conclusion, our results show that methionine supplementation during the first 4 days of the post-partum period in rabbits increases total litter size and the corporal weight of kits and is associated with an increase in blood concentration of IGF-1.

Short-term dietary concentrate supplementation during estrus synchronization treatment in beef cows increased IGF-I serum concentration but did not affect the reproductive response

The objective of this study was to evaluate if short-term dietary concentrate supplementation increased IGF-I serum concentration and resulted in a reproductive response during estrus synchronization treatment in non-lactating beef cows. Thirty non-lactating beef cows (Bos indicus × Bos taurus) were allocated to the same pastureland and fed native tropical grasses as a basal diet. Cows were synchronized using a 7-day CO-Synch plus controlled internal drug release (CIDR) protocol and received fixed time artificial insemination (FTAI). Cows were divided into two groups; the control group (n = 16) received 0.5 kg of concentrate/cow/day, whereas the supplemented group (n = 14) received 4.0 kg of concentrate/cow/day. The period of supplementation was 10 days from the day of CIDR insert to FTAI. The concentration of IGF-I increased (P < 0.05) in the supplemented group, while no significant changes were observed in the control group. Moreover, at the time of insemination, IGF-I serum concentrations were higher in supplemented cows compared with control cows (P < 0.05). Notably, metabolite and insulin concentrations did not differ (P > 0.05) between treatment groups or sampling day. The response to estrus induction, measured as estrus presentation, ovulation rate, and pregnancy rate, was similar between experimental groups (P > 0.05). In conclusion, our results indicated that supplementation with dietary concentrate for 10 days in non-lactating beef cows changed the endocrine milieu, specifically increasing IGF-I serum concentration. However, these endocrine changes did not affect response to estrous induction treatment.

Increased body condition score through increased lean muscle, but not fat deposition, is associated with reduced reproductive response to oestrus induction in beef cows

Energy reserve, estimated as body condition score (BCS), is the major determinant of the re-initiation of ovarian activity in postpartum cows. Leptin, IGF-I and insulin are positively related to BCS and are putative mediators between BCS and reproductive function. However, when BCS and body composition dissociates, concentrations of these metabolic hormones are altered. We hypothesized that increasing lean muscle tissue, but not fat tissue, would diminish the reproductive response to oestrus induction treatments. Thirty lactating beef cows with BCS of 3.10±1.21 and 75.94±12 days postpartum were divided in two groups. Control cows (n=15) were supplemented with 10.20 kg of concentrate daily for 60 days. Treated cows (n=15) were supplemented equally, and received a β-adrenergic receptor agonist (β-AA; 0.15 mg/kg BW) to achieve accretion of lean tissue mass and not fat tissue mass. Twelve days after ending concentrate supplementation/β-AA treatment, cows received a progestin implant to induce oestrus. Cows displaying oestrus were inseminated during the following 60 days, and maintained with a fertile bull for a further 21 days. Cows in both groups gained weight during the supplementation period (Daily weight gain: Control=0.75 kg v. β-AA=0.89 kg). Cows treated with β-AA had a larger increase in BCS (i.e. change in BCS: control=1 point (score 4.13) v. β-AA=2 points (score 5.06; P0.05) did not differ between groups. However, the number of cows displaying oestrus (control 13/15 v. β-AA 8/15; P<0.05) and the percentage cycling (control 6/8 v. β-AA 3/10; P=0.07) after progestin treatment and the pregnancy percentage at the end of the breeding period (control 13/15 v. β-AA 8/15; P<0.05) were lower in β-AA than control cows. In summary, the increase BCS through muscle tissue accretion, but not through fat tissue accretion, resulted in a lower response to oestrus induction, lower percentage of cycling animals and lower pregnancy percentage after progestin treatment; which was associated with a decrease in serum concentrations of leptin and IGF-I.

A meta-analysis of zilpaterol and ractopamine effects on feedlot performance, carcass traits and shear strength of meat in cattle

This study is a meta-analysis of the effects of the beta-agonists zilpaterol hydrochloride (ZH) and ractopamine hydrochloride (RAC) on feedlot performance, carcase characteristics of cattle and Warner Bratzler shear force (WBSF) of muscles. It was conducted to evaluate the effect of the use of these agents on beef production and meat quality and to provide data that would be useful in considerations on the effect of these agents on meat quality in Meat Standards Australia evaluations. We conducted a comprehensive literature search and study assessment using PubMed, Google Scholar, ScienceDirect, Scirus, and CAB and identification of other studies from reference lists in papers and searches. Searches were based on the key words: zilpaterol, zilmax, ractopamine, optaflexx, cattle and beef. Studies from theses obtained were included. Data were extracted from more than 50 comparisons for both agents and analysed using meta-analysis and meta-regression. Both agents markedly increased weight gain, hot carcase weight and longissimus muscle area and increased the efficiency of gain:feed. These effects were particularly large for ZH, however, fat thickness was decreased by ZH, but not RAC. Zilpaterol also markedly increased WBSF by 1.2 standard deviations and more than 0.8 kg, while RAC increased WBSF by 0.43 standard deviations and 0.2 kg. There is evidence in the ZH studies, in particular, of profound re-partitioning of nutrients from fat to protein depots. This work has provided critically needed information on the effects of ZH and RAC on production, efficiency and meat quality.