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.
1Facultad de Medicina Veterinaria,Universidad Nacional Autónoma de México,Av. Universidad 3000,Mexico D.F. 04360,México.
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A
Guzmán
1Facultad de Medicina Veterinaria,Universidad Nacional Autónoma de México,Av. Universidad 3000,Mexico D.F. 04360,México.
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Gonzalez-Padilla
1Facultad de Medicina Veterinaria,Universidad Nacional Autónoma de México,Av. Universidad 3000,Mexico D.F. 04360,México.
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Garcés-Yepez
2Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias,Hueytamalco Puebla,73580,México.
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Rosete-Fernández
2Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias,Hueytamalco Puebla,73580,México.
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RC
Calderón-Robles
3Department of Large Animal Clinical Sciences,Virginia Maryland Regional College of Veterinary Medicine,VA 24061,USA.
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Whittier
4Division of Animal Sciences,University of Missouri,Columbia,MO 65211,USA65211.
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DH
Keisler
1Facultad de Medicina Veterinaria,Universidad Nacional Autónoma de México,Av. Universidad 3000,Mexico D.F. 04360,México.
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CG
Gutierrez
D000273:Adipose Tissue / Q000187:drug effects*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001823:Body Composition / Q000187:drug effects; D002417:Cattle; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements; D004971:Estrus / Q000187:drug effects; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007774:Lactation; D020738:Leptin / Q000097:blood; D009132:Muscles / Q000187:drug effects*; D049590:Postpartum Period / Q000502:physiology; D011247:Pregnancy; D011897:Random Allocation; D000069466:Red Meat; D012098:Reproduction / Q000187:drug effects*; D015430:Weight Gain / Q000187:drug effects
D000318:Adrenergic beta-Agonists; D020738:Leptin; D007334:Insulin-Like Growth Factor I
      β-AA; IGF-I; energy status; insulin; leptin