Effect of feeding a high- or low-rumen escape protein supplement to dry Holstein cows and heifers within 3 weeks of calving on their productive and reproductive performance in the subsequent lactation

Pregnant Holstein heifers (450) and dry cows (417) within 3 weeks of calving (i.e., close up) were assigned to one of three groups. These groups were offered a low-CP (0.117 of DM) ration based on corn silage, alfalfa cubes, oat hay, corn and barley grain, or a medium-CP (0.144) ration, as the low-CP ration plus 1 kg per day per cow of a supplement (0.60 canola meal or rumen protected (RP) canola meal and 0.40 other), or a high-CP (0.166) ration, as the low-CP ration plus 2 kg per day per cow of one of the supplements. Use of bovine somatotropin (bST), movement through production groups, and breeding events were determined by the herd manager after calving. Production parameters were pooled to means for cows that successfully completed the lactation. The RP canola meal had an average 0.720 rumen undegraded crude protein content, based upon 16 h in situ incubation, versus 0.252 for untreated canola meal. Primiparous cows produced no more milk or milk components in their full lactation, or had higher peak milk yields, if supplemented with canola meal at any level from either source. However average body condition score in lactation was higher (P<0.01) for cows supplemented with RP canola meal. While multiparous cows supplemented with RP canola meal in their close up dry period peaked at higher levels of milk (P<0.01), they did not produce more milk or milk components during their full lactation. There is no indication that time in the close up group (between 1 and 19 days) had a substantive impact on milk production of multiparous cows, although primiparous cows produced 71 kg more milk (P<0.01) in their subsequent lactation for each extra day close up. In general, reproductive performance was not affected by any treatment and small differences among treatments in use of bST were judged to have been unlikely to have impacted milk production among treatments. These results are broadly consistent with results of others, and supportive of recent NRC [Nutrient Requirements of Dairy Cattle, 7th rev. ed., update. National Academy of Science, Washington, DC, USA, 2001] protein recommendations for close up heifers and multiparous cows. However the milk production lactation curves of cows of both parities differed between the period prior to bST use and the period of bST use. During the period prior to use of bST, cows supplemented with RP canola meal in the close up period outperformed those supplemented with untreated canola meal, whereas during the period of bST use the reverse occurred, primarily due to cows supplemented with RP canola meal being less responsive to bST. While no convincing explanation exists for this occurrence, its existence supports the high level of RUP determined in situ for the RP canola meal.