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Effect of feeding yeast culture on reproduction and lameness in dairy cows under heat stress

Bruno, R.G.S., Rutigliano, H., Cerri, R.L., Robinson, P.H., Santos, J.E.P.
Animal reproduction science 2009 v.113 no.1-4 pp. 11-21
dairy cows, cattle diseases, anovulation, conception, yeasts, health status, lactation, lameness, heat stress, warm season, Saccharomyces cerevisiae, female fertility, physiological response, pregnancy, disease severity, dietary supplements, diet therapy, disease incidence
Multiparous Holstein cows (n =717) from two dairy farms were blocked at calving by parity and previous lactation milk yield and, within each block, randomly assigned to one of two treatments: a diet containing no yeast culture (Control; n =359) or 30g/d of a culture of Saccharomyces cerevisiae (YC; n =358) from 20 to 140d postpartum. Only cows calving during months of heat stress, May-August were enrolled. Lameness score (1-5 scale) was evaluated at study enrollment and again at 100d postpartum. The body condition score (BCS, 1-5 scale) was evaluated at calving, 28, 58 and 140d postpartum. Cows received two injections of PGF₂α at 37 and 51d postpartum, and those observed in estrus were inseminated. Cows not in estrus were enrolled in a timed AI protocol at 65d postpartum and inseminated at 75d postpartum. Ovaries were examined by ultrasonography at 37 and 51d postpartum to determine whether estrous cycling had been initiated by the presence of a corpus lutem (CL) in at least one of the two examinations. Pregnancy was diagnosed at 31, 38 and 66d after the first AI and at 38 and 66d after the second and third AI. Diet did not affect time of onset of estrous cycles postpartum, and 8.2% of the cows were anovular. Detection of estrus in the 7d after the second injection of PGF₂α was similar for control and YC. For control and YC, conception rates 38d after AI at first (30.8% and 31.4%), second (39.3% and 35.1%) and third (25.8% and 30.6%) inseminations, and pregnancy losses did not differ, which resulted in similar median days to pregnancy and proportion of pregnant cows at 140d postpartum. Yeast culture did not affect incidence of lameness, but tended to reduce lameness score. Lame cows and anovular cows had lesser conception rates at first AI, and extended interval from calving to conception. A THI of 71 was identified as the critical point in which fertility was reduced in lactating dairy cows, although the sensitivity and specificity were minimal. Cows exposed to a THI>71 on the day of first AI had a 33% reduction in the rate of pregnancy resulting in extended interval to pregnancy. Feeding a yeast culture of S. cerevisiae had minor effects on lameness score, but no impact on reproduction of multiparous cows under heat stress.