8:00 am - 9:00 am
3-18J Agricultural/Forestry Centre, University of Alberta, Edmonton AB
A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Jennifer Haisan. This seminar is open to the general public to attend, either in person or online:
Meeting ID: 952 2665 8944
Thesis Topic: Effects of dietary starch allocation on feeding behaviours and production performance of dairy cows under various management scenarios
PhD with Dr. Masahito Oba.
Despite there being a large body of literature evaluating dietary strategies to support the metabolism of lactating cows, optimum dietary starch allocation, and resulting effects on milking performance and feeding behaviour are still unknown. The overall objective of this research was to determine the optimum dietary starch allocation during the calving transition period and under automated milking system (AMS) feeding management. We found that offering a high-starch prepartum diet increased dry matter intake and concentrations of insulin and glucose prepartum, and plasma free-fatty acid concentration and milk fat yield postpartum. Cows fed a high-starch diet postpartum had lower plasma free-fatty acid concentrations and serum haptoglobin. Feeding high-starch postpartum tended to increase milk yield when compared to feeding low-starch for cows fed the low-starch prepartum diet, but not high-starch pre-partum. When evaluating starch content of pellets fed separate from a complementary partial mixed ration (PMR), we found that offering a high-starch pellet resulted in cows consuming less PMR in the 3-hr following PMR delivery as compared to when a high-fiber pellet was fed. In addition, following PMR delivery, cows offered the high-starch pellet (with a high fiber PMR) consumed less PMR than those offered a high-fiber pellet (with a high starch PMR). When a high-starch pellet was fed, the duration that ruminal pH was below 5.8 was reduced compared to the high-fiber pellet. When evaluating the effects of a starch-based AMS pellet, offered at a high or low amount, when cows were fed a PMR formulated to meet requirements with low AMS pellet allocation, cows offered low reached target pellet intakes by wk 2; however, cows offered high, regardless of a moderate or rapid adaptation did not achieve target intakes. We found no difference in total dry matter intake regardless of pellet allocation; however, cows offered the low amount had greater milking frequency, milk yield and yields of milk fat, protein and lactose. We found no indication that cows fed either the high or low allocation experienced negative energy balance, and increased milk production was sustained to 8 wk of lactation for cows offered the low allocation. These results suggest that when formulating diets for cows managed with AMS, it is important to consider the composition of the PMR, not just the pellet, and that a high starch pellet may be fed without compromising animal performance or ruminal fermentation. In addition, it is possible to feed a high-starch diet postpartum regardless of prepartum dietary strategy; however, offering a starch-based pellet in excess of what the diet is formulated for when cows are managed with AMS may not be beneficial to animal performance.