Effects of feeding fodder beet or kale i

Context. Fodder beet (FB) is a widely used winter feed in New Zealand's southern regions due to its high yield, consistent quality, and environmental benefits. However, FB is low in crude protein, phosphorus and fibre, and a survey showed that many dairy farmers were concerned that feeding FB may have negative impacts on lifetime performance. Aim. To determine whether winter feeding FB or kale (Ka) to dairy cows, and then their heifer offspring at 1 and 2 years old, affects the heifer performance from birth until the end of their first lactation. Methods. In June–August 2017, pregnant dairy cows were fed FB or kale over winter and then 140 of the resultant heifer offspring were divided into four treatment groups at 9–11 months old according to their dam’s winter diet and offered either FB or kale, with pasture baleage. The groups were as follows (dam crop–heifer crop): FB-FB, FB-Ka, Ka-FB, Ka-Ka. The heifers’ subsequent performance (growth, stature, milk production, and reproduction) was measured to the end of their first lactation (May 2020), and blood hormonal status was monitored from May 2018 to May 2019. This observational study has its limitations, but is useful for generating hypotheses to test in more controlled research. Key results. Heifers grazing FB in winter (June–August) did not have lower blood plasma urea and phosphate concentrations than did heifers grazing kale, despite similar dietary crude protein contents. Treatments had no effect on milk production. However, the heifer liveweights were affected and there was an indication of poorer reproductive performance. The FB-FB relative treatment group had a lower average liveweight than the FB-Ka heifers from 1 to 2.8 years old. Conclusions. Although no impact on milk production for the first lactation was observed, the key results suggest possible negative impacts of feeding heifers FB during winter, particularly if their dam also wintered.