LACTATION PERSISTENCY AND PREDICTION OF TOTAL MILK YIELD FROM MONTHLY YIELDS IN EGYPTIAN BUFFALOES

M. Mohamed Abdelsabour Elmaghraby

Abstract
Factors affecting lactation persistency (LP) were studied using 525 lactations of 175 buffalo cows. LP was expressed as: LP1, average of proportions of each month's milk yield (MY) to preceding month's MY after peak yield is reached; LP2, ratio of 305-day MY (M305) to peak weekly yield; LP3, ratio of 2^nd 14 weeks MY to 1^st 14 weeks MY; LP4, ratio of descending MY to ascending MY; LP5, rate of decrease in weekly MY from peak week yield to last week yield, and LP6, the coefficient of variation (%) among successive weekly yields. Period of calving affected significantly LP2 and LP3. Summer and spring calvings were associated with high LP (LP2, LP3, LP6). Unexpectedly, first parity cows had the least LP, and those in their 4^th lactation were the most persistent. LP deteriorated with shorter days open indicating negative effect of early pregnancy. Heritability ranged from 0.02 (LP6) to 0.33 (LP2). Except LP4 and LP6, LP had moderate to high correlation with M305 and days in milk. Maximum R2 improvement procedure was used to predict M305 from monthly MY (n, 294). First, 3^rd and 6^th monthly MY can be pooled to precisely predict M305 (R2, 0.76). Inclusion of more variables in the model caused little improvement in predictability. In conclusion, LP of the study herd was low. It is likely that avoiding short days open, and improving heifer raising program and 1^st lactation management, in addition to genetic selection, particularly for LP2, would improve LP.

Key words: Buffalo, lactation persistency, prediction of total milk yield