| As a predictor of the lifetime performance and longevity of dairy cows,it is particularly important to study the related factors that affect the performance of first-lactation cows.In this study,2342 Holstein cows were selected to study the effects of birth weight,average daily gain before weaning,weaning weight,birth season,calving season and age at first calving on the performance of first-lactation.The results showed that:Experiment 1:Effects of related factors on milking performance of first-lactation cows.1.With the birth weight of calves increasing(35.00-50.00)kg,the 305-day milk yield of firstlactation cows increased;With the increase of the daily gain before weaning,the milk yield at 305 days had a decreasing trend,but the differences were not significant(P>0.05).2.The peak milk yield(40.80±6.22)kg of first-lactation cow born in spring was significantly higher than that in summer and autumn(P<0.01),the 305-day milk yield(10219.97±1418)kg of calves born in autumn was the highest,and the difference was significant(P<0.05);The percentage of milk protein(3.51±0.36)%in the first-lactation of calves born in spring was significantly higher than that in other seasons(P<0.01),and there was no significant difference in milk fat percentage(P>0.05).3.In the calving season of heifers,the peak milk yield of first-lactation cow when calving in spring(40.58±6.11)kg was significantly higher than that in summer and winter(P<0.01);The percentage of milk protein when calving in spring(3.50±0.34)%was significantly higher than that in other seasons(P<0.01),the 305-day milk yield of first-lactation cow when calving in autumn(10143.69±1590)kg was higher than that in other seasons,and the 305-day milk yield when caving in winter(9419.25±1400)kg was lower than that in other seasons,and the differences were extremely significant(P<0.01).4.With the increase of age at first calving,the peak milk yield and 305 day milk yield of the first-lactation gradually increased.The 305-day milk yield of the first-lactation with the age at first calving in 665-860 days was significantly higher than that in less than 665 days(P<0.01).Experiment 2:Effects of related factors on the reproductive performance of first-lactation cows1.The voluntary waiting day(59.49±6.82)of first-lactation cows with birth weight of 45.0050.00 kg was less than that with birth weight<35.00 kg(60.74±5.64),and the differences were extremely significant(P<0.01).The voluntary waiting day with 0.70-0.80kg daily gain before weaning was also significantly shorter,and the difference was very significant(P<0.01).2.Compared with other seasons in the birth season,the voluntary waiting age(422.55±47.50)for young heifers and the voluntary waiting day(58.69±4.32)for first-lactation cows when born in autumn was the shortest,and the difference was very significant(P<0.01).3.The voluntary waitting day(60.17±6.66)of the first-lactation cow with the age at first calving in 665-730 days was the shortest,and the difference was very significant(P<0.01).The voluntary waitting day(62.52±4.38)of the first-lactation cow with the age at first calving in ≤665 days was the longest,and the difference was very significant(P<0.01).Experiment 3:Effects of related factors on postpartum health of first-lactation cows.1.The incidence of ketosis and dystocia was the lowest in young cattle calving in winter,and the differences were significant(P<0.05).2.With the increase of age at first calving,the incidence of postpartum in the first-lactation cows gradually decreased,and the difference was significant(P<0.05).When age at first calving in≤665 days and≥860 days,the dystoia rate was higher,and the difference was very significant(P<0.01).In conclusion,during the process of replacement raising,birth weight,average daily gain before weaning,birth season,calving season,and age at first calving can affect the performance of first-lactation cows in varying degrees. |
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