Associations between age at first calving and subsequent lactation performance in UK Holstein and Holstein-Friesian dairy cows

Abstract

Lactation records from 396,534 pedigree Holstein and Holstein-Friesian primiparous cows from 6,985 UK milk recorded herds, calving for the first time during the period between the 1st of January 2006 and the 31st of December 2008, were examined in order to determine the associations between age at first calving (AFC) and subsequent production, udder health, fertility and survivability parameters. Heifers were grouped by AFC into single month classes ranging from 21 to 42 months. Mixed effects multivariable regression modelling was used for data analysis. Mean and median AFC were 29.1 and 28 months respectively. Within the study, only 48,567 heifers (12.3% of the studied population) calved for the first time at 24 months of age or younger. 162,157 heifers (40.9%) were 30 months or older at their first calving. An increased AFC was associated with increased first lactation milk, fat and protein yields. The lowest predicted mean 305-day yield (6,617kgs; 95% confidence interval (CI): 6,546-6,687 kgs) was recorded for the 21 month AFC class, significantly lower than any other class. The 36 month AFC class had the highest predicted mean (7,774 kgs; 95% CI: 7,737-7,811 kgs). However, an increased AFC was also associated with increased calving interval and increased first lactation somatic cell count (SCC). Animals calving at 21 months had a predicted mean lactation SCC of 72,765 (95% CI: 68427-77378). Animals calving at 36 months of age had a predicted mean lactation SCC of 86,648 (95% CI: 84,499-88,853). Importantly, an increased AFC was also associated with decreased lifetime daily milk yield and decreased likelihood of calving for a second successive time. Animals calving at 22 months of age had a predicted mean daily lifetime milk yield of 15.24 kgs (95% CI: 15.06-15.35); animals calving at 36 months of age had a predicted mean daily lifetime milk yield of 12.83 kgs (95% CI: 12.76-12.91). Our results highlight the importance of achieving a lower age at first calving which was here associated with improved udder health, increased lifetime daily milk yield, improved reproductive performance and increased likelihood of calving for a second time.

Fig 1. Age at first calving of UK Holstein and Holstein-Friesian heifers.

Distribution of age at first calving (AFC) for pedigree Holstein and Holstein-Friesian milk recorded heifers calving in the UK between 01/01/06 and 31/12/08.

Fig 2. Age at first calving and first lactation milk yield.

Predicted means (± 95% confidence intervals) obtained from mixed effects multivariable regression modelling for first lactation (305-day) milk yield (kgs) by different age at first calving (AFC) class.

Fig 3. Age at first calving and first lactation fat and protein yield.

Predicted means (± 95% confidence intervals) obtained from mixed effects multivariable regression modelling for first lactation (305-day) fat and protein yield (kgs) by different age at first calving (AFC) class.

Fig 4. Age at first calving and recorded lifetime daily yield.

Predicted means (± 95% confidence intervals) obtained from mixed effects multivariable regression modelling for recorded lifetime daily yield (milk kgs) by different age at first calving (AFC) class.

Fig 5. Age at first calving and first lactation somatic cell count.

Back-transformed predicted means (± 95% confidence intervals) obtained from mixed effects multivariable regression modelling for first lactation (305 day) log somatic cell count (cells/ml) by different age at first calving (AFC) class.

Fig 6. Age at first calving and calving interval.

Back-transformed predicted means (± 95% confidence intervals) obtained from mixed effects multivariable regression modelling for calving interval (days) by different age at first calving (AFC) class.