PHYSIOLOGY AND MANAGEMENT Increased Milk Production Versus Reproductive and Energy Status of High Producing Dairy Cows1 R. O. HARRISON,2 S. P. FORD, J. W. VOUNG,3 A. J. CONLEV,4 and A. E. FREEMAN Department of Animal Science Iowa State University Ames 50011 ABSTRACT
(Key words: milk production, reproductive status, energy balance)
Two groups of 10 Holstein cows were chosen by pairs from a 20-yr genetic selection project that used either breed average or breed high sires chosen only for Predicted Differences in milk production. Milk production (305-d mature equivalent) was 10,814 kg and 6912 kg for the high and average groups of cows. Days to first visual estrus and number of ovulations before first visual estrus were greater for the high versus the average group (66 vs. 43 d and 1.6 vs..7 ovulations). No differences were significant between groups for the interval from parturition to uterine involution or for days to first ovulation. Energy balance was less for the high group during wk 1, 2, 10, and 11. Plasma glucose concentration was lowest during wk 2 for both groups, and nonesterified fatty acids and /3-hydroxybutyrate were greatest for both groups during wk 1 and 2. Liver glycogen content was lower at d 15 postpartum for the high group, and liver triglyceride content was greater on d 30 for the high group. The data for reproductive functions support the concept that high milk production is antagonistic to expression of estrous behavior but not to reactivation of ovarian function.
INTRODUCTION
Received August 7, 1989, AccePted May 9. 1990. IJoumal Paper Number J-13591 of the Iowa Agriculture and Home Economics Experiment Station, Ames; Projects Number' 2504.2443. and 1053. The data are from a dissertation submitted to Iowa State University by R. O. Harrison to partly fulfill requirements for the Ph.D. degree. 2Nutrition Professionals. Inc.• Route 3. Box 9. Hortonvill~ WI" 54944. "Repnnt requests. 4Green Center. University of Texas Health Science Center, 5323 Harry Hines Blvd.• Dallas 75235.
1990 J Dairy Sci
73:274~2758
High milk production per cow is one of the most important factors contributing to profitability of a dairy farm, and genetic selection for increased milk production has been the most consistent way to increase production per cow. Mean milk production per cow increased from 3400 kg in 1962 to 6252 kg in 1987. With major emphasis on selection for increased milk production, there has been strong interest in the resulting effects on reproduction. Heritability for milk production is about .25, but reproductive traits have a heritability of
(Key words: milk production, reproductive status, energy balance)
Two groups of 10 Holstein cows were chosen by pairs from a 20-yr genetic selection project that used either breed average or breed high sires chosen only for Predicted Differences in milk production. Milk production (305-d mature equivalent) was 10,814 kg and 6912 kg for the high and average groups of cows. Days to first visual estrus and number of ovulations before first visual estrus were greater for the high versus the average group (66 vs. 43 d and 1.6 vs..7 ovulations). No differences were significant between groups for the interval from parturition to uterine involution or for days to first ovulation. Energy balance was less for the high group during wk 1, 2, 10, and 11. Plasma glucose concentration was lowest during wk 2 for both groups, and nonesterified fatty acids and /3-hydroxybutyrate were greatest for both groups during wk 1 and 2. Liver glycogen content was lower at d 15 postpartum for the high group, and liver triglyceride content was greater on d 30 for the high group. The data for reproductive functions support the concept that high milk production is antagonistic to expression of estrous behavior but not to reactivation of ovarian function.
INTRODUCTION
Received August 7, 1989, AccePted May 9. 1990. IJoumal Paper Number J-13591 of the Iowa Agriculture and Home Economics Experiment Station, Ames; Projects Number' 2504.2443. and 1053. The data are from a dissertation submitted to Iowa State University by R. O. Harrison to partly fulfill requirements for the Ph.D. degree. 2Nutrition Professionals. Inc.• Route 3. Box 9. Hortonvill~ WI" 54944. "Repnnt requests. 4Green Center. University of Texas Health Science Center, 5323 Harry Hines Blvd.• Dallas 75235.
1990 J Dairy Sci
73:274~2758
High milk production per cow is one of the most important factors contributing to profitability of a dairy farm, and genetic selection for increased milk production has been the most consistent way to increase production per cow. Mean milk production per cow increased from 3400 kg in 1962 to 6252 kg in 1987. With major emphasis on selection for increased milk production, there has been strong interest in the resulting effects on reproduction. Heritability for milk production is about .25, but reproductive traits have a heritability of
