UDK xxxx xxxx xxxx EFFECT OF CALVING INTERVAL ON MILK YIELD IN JERSEY COWS UNDER CONDITIONS OF SMALL FAMILY FARMS IN ALBANIA

Sažetak Effect of calving interval on 305 day milk yield for first three lactations was studied in order to increase efficiency of selection schemes and to more efficiently manage Jersey cows that have been raised on small scale family farms in Albania. Results obtained by processing data of 1476 cows, managed in 935 small scale family farms, pointed out that current calving interval significantly affects on milk production for first three lactations (p<0.05). Preceding calving interval affected 305 day milk yield (p<0.05) in second lactation only. Linear regression model accounted for 20-25 % of the total variance of 305 day milk yield. Extension of calving interval over 420, 430, 450 days for first, second and third lactations respectively, did not increase milk production when converted to 305 day lactation. Stochastic relations between calving interval and calving age and month are moderated. Values of Pierson's correlation coefficients ranged 0.38 to 0.69. Adjustment of milk production in order to reduce effect of calving interval on total phenotypic variance of milk yield is valid for first lactation only. Adjustment of 305 day milk yield for second and third lactations in order to reduce effects of factors "calving age and month" brings about, at the same time, elimination of calving interval effect. Ključne riječi: milk production, small family farm, calving interval Uvod Length of calving interval is one of non genetic factors affecting milk yield in cattle. It is known that length of calving interval depends on length of days open, whose variance is conditioned by different environmental factors such as: feeding, production system, AI technician's skills, management skills of farmer etc. To make possible an efficient selection of cows, the literature recommends that along side different adjustments, 305 day milk yield should be adjusted to reduce effect of calving interval on its total variance (H a n s e t , 1978; L e r o y , 1980; K u m e , 1989; J a m r o z i k , 1997; B i ç o k u , 1995; N e b e l , 2001)