Abstract
The objective of the present study was to determine whether the day of the week in which delivery occurs and herd size impact reproductive performance. Reproductive information was recorded for eighteen months from 23 small-scale dairy farms (833 calvings) located in Los Altos of Jalisco state. Analysis of variance and logistic regression analyses were performed to determine the effect of independent variables (day of delivery and herd size) on continuous variables (days at first service (DPS) and days open (DA)) and dichotomous variables (assisted calving), respectively. In big farms (≥33 cows) there were no differences (P> 0.05) due to delivery day on DPS. In small farms (<33 cows), cows that gave birth on Wednesday and Thursday had higher DPS (106.1±10.1 and 120.8±11.5) (P <0.05). Cows that gave birth on Saturday in big farms had higher DA (136.4 ± 7.0) as compared to those who delivered on other days (P <0.05). Finally, small farms had twice as many assisted calvings (21.0%) than large herds (10.4%) during weekends (Friday to Sunday) (P <0.05). In conclusion, big farms are less affected by the delivery day effect while small farms reported twice as many assisted calvings during weekends.
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