Challenging the paradigm of one calf per year : Consequences of extended lactations for individual dairy cows

Abstract

In most dairy systems, cows are managed to have a calf every year. A yearly calving is expected to maximize milk production due to the related yearly lactation peak. During the transitions around calving, cows have an increased risk for diseases. Lactations could be deliberately extended by extending the voluntary waiting period for insemination (VWP). This increases the calving interval (CInt) and reduces the frequency of calvings. A longer lactation and longer period in late lactation, however, may be related with a lower milk production, and a risk for fattening at the end of the lactation. This project aimed to evaluate the consequences of extended lactations for milk production, fertility, health, metabolism, and economic performance of individual dairy cows, by using both data from commercial farms and an experimental approach. Additionally, the aim was to identify cow factors that determine the response of individual cows to an extended lactation. At 13 commercial dairy farms where the VWP was deliberately extended for part of the herd, farmers selected their high-producing cows for an extended lactation, as indicated by the greatest 305-d production in the groups with the longest CInt. Milk production per day of CInt, however, was not always greatest for these cows. A longer CInt, but not a longer calving to first service interval, was related with an increased number of inseminations. In an experimental setting, the VWP was extended until 125 or 200 days for 41 primiparous (PP) and 113 multiparous (MP) cows. The VWP could be extended until 200 days for PP cows and until 125 days for MP cows with no effect for milk production per day of CInt. Multiparous cows with a VWP of 200 days had a lower milk production per day of CInt compared with MP cows with a shorter VWP. The lactation persistency between day 100 in lactation and the start of dry-off was improved for cows with a VWP of 200 days compared with cows with a VWP of 50 days. At the end of the extended lactation, an extended VWP resulted in a lower milk production at dry-off, which maybe be beneficial for udder health, but was also related with body fattening of MP cows. At the start of the next lactation, MP cows with a VWP of 200 days had a greater body condition score, a more severe negative energy balance, and a greater plasma non-esterified fatty acid concentration compared with MP cows with a VWP of 50 days, indicating an increased risk for metabolic disorders in the next lactation. For PP cows, the VWP did not affect milk yield or body condition at the end of the lactation or metabolic status at the start of the next lactation. Therefore, PP cows and MP cows with a high milk production and a low body condition before insemination may be more suitable for an extended VWP. Cows with a VWP of 200 days had lower total yearly revenues, but also lower total yearly costs, compared with cows with a VWP of 50 days. The yearly net partial cashflow was not significantly associated with the VWP, possibly partly due to the great variation among cows. To con...

Extended voluntary waiting period before first insemination in primiparous dairy cows : effects on milk production, fertility, and health

“…For this reason, it is of critical importance to investigate new possible management routines to allow for flexibility and thereby resilience, and to question old 'truths'. One of the practices that has been challenged in several studies over many years Burgers 2022) is that a cow should have one calf per year to be most profitable Steeneveld & Hogeveen, 2012).…”