Guzmán A, Gonzalez-Padilla E, Garcés-Yepez P, Rosete-Fernández J V, Calderón-Robles R C, Whittier W D, Keisler D H, Gutierrez C G
1Facultad de Medicina Veterinaria,Universidad Nacional Autónoma de México,Av. Universidad 3000,Mexico D.F. 04360,México.
2Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias,Hueytamalco Puebla,73580,México.
Animal. 2016 Oct;10(10):1706-13. doi: 10.1017/S175173111600063X. Epub 2016 Apr 22.
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.
能量储备，以体况评分（BCS）来估算，是产后母牛卵巢活动重新启动的主要决定因素。瘦素、胰岛素样生长因子-I（IGF-I）和胰岛素与BCS呈正相关，并且是BCS与生殖功能之间的假定介质。然而，当BCS与身体组成分离时，这些代谢激素的浓度会发生改变。我们假设增加瘦肉组织而非脂肪组织，会减弱对发情诱导处理的生殖反应。30头产后75.94±12天、BCS为3.10±1.21的泌乳期肉牛被分为两组。对照组母牛（n = 15）每天补充10.20千克精饲料，持续60天。处理组母牛（n = 15）给予等量补充，并接受一种β-肾上腺素能受体激动剂（β-AA；0.15毫克/千克体重），以实现瘦肉组织而非脂肪组织的增加。在精饲料补充/β-AA处理结束12天后，母牛接受孕激素植入以诱导发情。表现出发情的母牛在接下来的60天内进行人工授精，并与一头可育公牛一起饲养21天。两组母牛在补充期均体重增加（日增重：对照组 = 0.75千克对β-AA组 = 0.89千克）。接受β-AA处理的母牛BCS增加幅度更大（即BCS变化：对照组 = 1分（评分4.13）对β-AA组 = 2分（评分5.06；P<0.05））。处理后血清中瘦素和IGF-I的浓度（对照组 = 5.1±1.0纳克/毫升对β-AA组 = 3.2±0.8纳克/毫升；P<0.05）在两组间无差异。然而，孕激素处理后表现出发情的母牛数量（对照组13/15对β-AA组8/15；P<0.05）以及发情周期百分比（对照组6/8对β-AA组3/10；P = 0.07）和繁殖期末的妊娠率（对照组13/15对β-AA组8/15；P<0.05），β-AA组均低于对照组母牛。总之，通过增加肌肉组织而非脂肪组织来提高BCS，会导致对发情诱导的反应降低、发情周期动物百分比降低以及孕激素处理后的妊娠率降低；这与血清中瘦素和IGF-I浓度的降低有关。
