The effect of winter diet on pre-partum weight gain and post-partum milk production of grazing primiparous animals

Forage brassicas, such as kale, are considerably cheaper as a winter feed than grass silage and concentrates, which are 2 and 4 times more expensive than grazed grass, respectively. An experiment was undertaken to investigate the effect of offering four different winter diets on heifer bodyweight (BW) and body condition score (BCS) during the winter period. Subsequent milk production performance was monitored when all heifers were managed similarly post-partum on a pasture-based system. One hundred Holstein-Friesian replacement heifers were balanced on the basis of age (639+/-20.5 days), projected calving date (23 February +/- 22.0 days), BW (459+/-43.8 kg) and BCS (3.21+/-0.215) and randomly assigned to one of four feeding treatments. The four treatments were i) indoors offered grass silage only (SO), ii) indoors offered grass silage plus 2 kg concentrate per day for a 46-day period (SC), iii) outdoors offered 70% kale + 30% grass silage (70K), and iv) 100% kale diet (100K). The experiment commenced on 15 November and heifers remained on their treatments until a week before calving. Following the winter period, daily weight gain was similar for the SC and 70K treatments (1.10 kg heifer(-1) day(-1)), weight gain was lower for the SO treatment (0.96 kg heifer(-1) day(-1)), the weight gain of the 100K heifers was significantly (P < 0.001) lower than all other treatments (0.78 kg heifer(-1) day(-1)). There was no difference in cumulative milk yield or milk solids yield between treatments. The results from this study indicate that over-winter diet does not affect subsequent milk production performance.