Mammary Growth Pattern in Goats During Pregnancy and Lactation

Nine groups of five dairy goats from four breeds, with each breed represented at least once in each group, were in our experiment to measure mammary gland growth. Groups were virgins, days 90 to 100 pregnancy, 5 days prepartum (145 days pregnancy), 1 or 2 days prepartum, and 1 or 2, 5, 10, 15, and 30 days in lactation. Virgins were 19 mo old while all others had one pregnancy and lactation prior to experiment. Indices of mammary growth included untrimmed and trimmed wet weights of udders, dried fat-free tissue weights, deoxyribonucleic acid and ribonucleic acid contents. Each index was in a regression equation best to describe the pattern of mammary growth. These included linear, quadratic, cubic, and exponential model Y = AebX in which Y was the index of mammary growth and X was the day of pregnancy. Total deoxyribonucleic acid was the best index of mammary growth with a correlation of .95 in the exponential model. The predictive equation for total deoxyribonucleic acid in milligram was Y = 167e.019X on a daily basis, and the rate of growth on a monthly basis was .57. Mammary growth in goats continued into early lactation, peaking at day 5. Ribonucleic acid doubled on the day after parturition, which reflected the rapid increase in protein synthesis at this time.