DOGMA IN REPRODUCTIVE MANAGEMENT OF DAIRY HERDS QUESTIONED

Cow fertility is vital on every dairy farm, as reduced fertility results in extended calving intervals, fewer lifetime lactations per cow, and higher replacement rates, with dire consequences to both biological and economic sustainability. Optimising fertility traits, such as calving interval, age at first calving, conception rates and days open must therefore be priority in cow management. This also has direct bearing on costs: input costs continue to rise and milk prices remain volatile, thus improving reproductive performance can directly influence margins through reduced culling, improved milk yield per day of herd life and better utilisation of feed resources, especially in TMR systems. To further investigate these interactions, the author cited examined the impact of optimising fertility traits on the profitability of Holstein herds operating within a TMR production. In the study, the impact of fertility traits such as inter-calving period (ICP) and age at first calving (AFC) on the profitability of Holstein herds that were fed a total mixed ration (TMR), were investigated.

To determine the impact of AFC and ICP on profitability, 4 949 historical records from three Holstein Friesian herds were used. These records included milk, butterfat and protein production, birth dates, calving dates, and dates when lactations were terminated. On-farm data were obtained from the three herds that were used in this study. The on-farm data included ration composition, cost of rations, actual body weights per age group, dry matter intake (DMI) per age group and general management parameters involved in calf rearing and heifer- and dry cow management. Nett income over feed cost was calculated for each cow for each lactation. This was done to determine a total income by using a milk price structure that reflects the pricing structure in the area where the three herds are situated.  The on-farm data and the calculated weights were used to obtained the dry matter intake of each cow and this was used to calculate a total cost of feed. The nett difference between the two values were used to determine the nett income over feed cost. In a separate investigation, the impact of extended voluntary waiting periods (VWP) on the net income over feed cost and fertility were also investigated in a Holstein herd where the VWP was adapted over a period of 10 years. The production records of 2 204 and fertility records of 750 Holstein cows from this herd were available for this investigation. In the herd the VWP was increased from 45 days to 60 days, and then to 80 days for second and later lactation cows and 100 days in first lactation cows.

The results showed: (1) Rearing cost of heifers showed a positive relation with AFC, which also impacts on the nett income over feed cost for the first lactation; (2) Heifers that were older at first calving were less profitable than younger heifers; (3) The extension in VWP did not have a significant impact on fertility traits. The Pearson correlations between VWP, straws per conception (SPC) and days from first insemination to conception, were non-significant. The data furthermore indicated that the extended VWP contributed to longer lactation lengths, which was beneficial to the profitability of the herd: For a one-day increase in days in milk (DIM), the net income above feed cost increased by R 89.66. First lactation cows benefited most from the extension of the length of lactation, as for every one-day increase in DIM, the net income over feed cost increased by R 96.73.

It was concluded that heifers should calve at less than 25 months for the first time for better profitability. The data also indicated that cows with longer ICP’s tend be more profitable, with cows with a ICP of more than 400 days being more profitable than cows with the more traditional 365-day ICP. Apart from more milk above feed costs being produced, the vulnerable situations at and immediately beyond calving with cost implications, is another reason for this finding. It was clear that an extended VWP that caused an extension in days in milk of lactation, should be beneficial to the profitability of TMR fed dairy herds, casting doubt on generally accepted dogma.