A comparison of Barkant turnips and Superchow sorghum for summer milk production

Abstract

Barkant turnips and Superchow sorghum were compared as summer-autumn crops for lactating cows, in a 2 × 3 factorial experiment fed at 3 levels (0, 4 and 8 kg DM/cow/day) to supplement pasture offered at a constant allowance of 25 kg DM/cow/ day. Sixty lactating twin cows were used in 2 experimental periods in January and March 1996. Pasture and crop intakes were estimated by the alkane, and pre- and post-grazing, techniques. Feeding either 4 or 8 kg DM/cow/day increased milksolids (MS) yield by 25% for turnips and 15% for sorghum compared with pasture alone. Turnips gave responses of 42.5 and 50 g MS/kg DM offered, at the lower allowance, in summer and autumn respectively; compared with 25 g MS/kg DM in both seasons for sorghum. Crop intakes were lower on sorghum than turnips and were only partially compensated for by increased pasture intakes on the former. For both crops, increasing allowance from 4 to 8 kg DM/cow/day did not increase daily MS yield. The cows grazing sorghum were 8 and 15 kg heavier than either the turnip or pasture-fed cows in summer and autumn respectively. Substitution rates for both crops were higher (0.72- 0.87) in summer than in autumn (0.35-0.45). This means that although both crops will have a "pasture sparing" effect in summer they will not contribute much to increased per cow intake. Keywords: alkanes, crop intake, dairy cows, milksolids, milk yield, pasture intake, sorghum, turnips Introductio