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

Abstract

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; P < 0.05), as a result of muscle accretion (i.e. change in muscle depth: control 0.21 cm v. β-AA 0.97 cm; P < 0.05) but not adipose tissue (i.e. change in back fat depth; control 0.13 cm v. β-AA −0.06 cm; P < 0.05). The changes in body composition in β-AA cows were associated with a reduction in serum concentrations of IGF-I (25.4%) and leptin (27.9%), without observed changes in insulin. Ovulation and pregnancy to 1st service (P > 0.05) 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.Keywords: β-AA, energy status, IGF-I, insulin, leptin ImplicationsReproductive function in postpartum beef cows is regulated by energy status and positively associated with serum concentrations of leptin, insulin and IGF-I. β-adrenergic receptor agonist (β-AA) treatment results in muscle accretion, whilst reducing fat deposition. The reduction in body fat, despite the overall BW gain, results in lower leptin and IGF-I concentrations and a suboptimal response to an oestrus induction programme and pregnancy percentage after breeding. He...

Variations in the Temperature-Humidity Index and Dorsal Fat Thickness during the Last Trimester of Gestation and Early Postpartum Period Affect Fertility ofBos indicusCows in the Tropics

“…The THI for each farm was calculated monthly considering the average environmental temperature and relative humidity of the period in which the study was conducted, applying the equation proposed by García-Ispierto et al [ 16 ]: where THI is the temperature-humidity index; T is the mean temperature expressed in °C; and RH is the average relative humidity expressed in percentage. Unfortunately, wind speed and solar radiation were not considered; it was assumed that THI was the best indicator of animal heat stress [ 12 – 14 ]. As it was an observational study in private farms, data on climatic factors were taken from weather stations nearby not further than 10 km.…”

“…Fat thickness (FAT) has been shown to be a reliable indicator of the level of energy reserves in the animal [ 11 ]. There is evidence suggesting that the FAT during the last trimester of pregnancy is associated with reproductive capacity [ 12 – 14 ]. Therefore, early resumption of ovarian activity is closely related to the ability of the dam to recover from the negative energy balance caused by stress during calving [ 8 ] and the inability to cope with extreme environmental conditions [ 15 ].…”