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- Title
Effects of body condition on measures of intramuscular and rump fat, endocrine factors, and calving rate of beef cows grazing common bermudagrass or endophyte- infected tall fescue.
- Authors
Looper, M. L.; Reiter, S. T.; Williamson, B. C.; Sales, M. A.; Hallford, D. M.; Rosenkrans Jr., C. F.
- Abstract
Multiparous beef cows were managed to achieve marginal (BCS = 4.7 ± 0.07; n = 106) or good (BCS = 6.6 ± 0.06; n = 121) body condition (BC) to determine the influence of forage environment on BW and BC changes, intramuscular fat percentage (IMF), rump fat (RF), and serum hormones during 2 yr. Cows within each BC were randomly assigned to graze either common bermudagrass (CB; n = 3 pastures/yr) or toxic endophyte-infected tall fescue (EI; n = 3 pastures/yr) during a 60-d breeding season. Blood samples were collected at d 0, 30, and 60 of the breeding season, and serum concentrations of prolactin (PRL), IGF-I, and cortisol (CORT) were quantified; PRL and progesterone (P4) also were quantified 10 d before the breeding season (d -10). Body weight and BCS were recorded during the breeding season (d 0, 30, and 60). Cow IMF and RF were measured via ultrasonography at the start and end of the breeding season. Cows with increased (>1 ng/mL) P4 at the beginning of the breeding season (cyclic) had greater (P < 0.02) concentrations of PRL on d 30 and 60 compared with anestrous cows. A forage environment × BC interaction tended (P = 0.07) to influence PRL. Cows grazing CB independent of BC had increased PRL compared with cows grazing EI. Prolactin was decreased in good-BC cows grazing El compared with cows grazing CB, and cows in marginal BC grazing El had the least concentrations of PRL. Concentrations of IGF-I were similar (P > 0.10) among good- and marginal-BC cows grazing CB, as well as good-BC cows grazing El; however, marginal-BC cows grazing El had reduced (P < 0.04) concentrations of IGF-I compared with all other groups. Cows in marginal BC grazing CB gained (P = 0.02) the most BW during the breeding season, whereas good-BC cows grazing El gained the least amount of BW. Marginal-BC cows grazing CB tended (P 0.06) to increase BC during the breeding season, whereas good-BC cows grazing either CB or El lost BC. Rump fat tended (P = 0.07) to increase during the breeding season in marginal-BC cows compared with cows in good BC. Calving rates were similar (P > 0.10) among good- (82%) and marginal- (84%) BC cows grazing CB, and good-BC cows grazing El (79%); however, marginal-BC cows grazing El had a reduced (P = 0.04) calving rate (61%). Cattle grazing El during the breeding season lost BC. That reduction in BC maybe communicated to the pituitary via hormones that include IGF-I or PRL or both, resulting in decreased calving rates.
- Subjects
ANIMAL breeding; COWS; BERMUDA grass; ENDOPHYTES; FAT; PROLACTIN
- Publication
Journal of Animal Science, 2010, Vol 88, Issue 12, p4133
- ISSN
0021-8812
- Publication type
Article
- DOI
10.2527/jas.2010-3192