تأثير عوامل تغذيه‌اي دوره خشكي بر كميت و كيفيت آغوز گاو‌هاي شيري هلشتاين در گاوداري‌هاي منتخب ايران

The objective of this study was to eva‎luate the effects of nutritional an‎d non-nutritional factors during the dry period on colostrum quantity an‎d quality in dairy cows from selec‎ted dairy farms in Iran. Data related to dry cow rations were collected from dairy farms located in Mashhad, Isfahan, Yazd, an‎d Tehran, an‎d ration compositions were analyzed using CPM-Dairy software. Based on the obtained results, a database was developed including the average nutrient composition of rations during the far-off an‎d close-up periods, along with non-nutritional factors such as calf birth weight, gestation length, days pregnant at dry-off, calf sex, parity, an‎d calving month. Multiple regression models were applied to eva‎luate the effects of these factors on colostrum quantity an‎d quality, while herd code was included as a fixed effect to control for herd-related differences. The results demonstrated that, in the final colostrum yield model, among the nutritional factors only metabolizable energy during the far-off period had a significant positive effect on colostrum yield (P = 0.002). Among the non-nutritional factors, days pregnant at dry-off had a negative effect, whereas gestation length an‎d calf birth weight had positive effects on colostrum yield. In addition, some calving months were associated with lower colostrum production compared with the reference month. From the third parity onward, parity had a significant negative effect on colostrum yield, an‎d multiparous cows produced less colostrum than primiparous cows. To investigate the indirect effects of nutrition on colostrum yield, a separate regression model was developed for calf birth weight. In this model, metabolizable energy during the far-off period had a significant positive effect (P = 0.046), whereas metabolizable energy during the close-up period showed a tendency toward significance (P = 0.064) for calf birth weight. In the colostrum quality model (Brix percentage), only non-nutritional factors were included because dry period diets were uniform in farms with regular Brix records. The results indicated that parity had a strong positive effect on Brix percentage, while an inverse relationship was observed between colostrum volume an‎d Brix percentage. Furthermore, calving month significantly affected Brix values, with higher Brix percentages observed during some colder months of the year. Overall, the findings suggest that nutritional factors during the dry period exert a weaker influence on colostrum yield compared with non-nutritional factors, with these effects being mediated directly through metabolizable energy during the far-off period an‎d indirectly through their influence on calf birth weight.

غلامرضا قرباني خراجي , فرزاد هاشمزاده

عباس رجائي راد

سعيد انصاري مهياري , نفيسه سلطاني زاده