Use of canola meal as a protein source in pelleted starter mixtures for dairy calves
The broad hypothesis for the series of studies conducted within my Ph.D. research was that canola meal (CM), when supplied in pelleted starter mixture, will be an adequate protein source for dairy calves supporting body weight gain and gastrointestinal tract (GIT) development, possibly further enhancing those processes when included with other dietary supplements or through processing of CM. Five studies were conducted with a global objective to determine whether the use of CM as protein source in calf starters, when included in combination with other supplements or processing, could help substantiate satisfactory calf growth and GIT development. The first study assessed the different temperatures of heat-treating CM on ruminal and intestinal nutrient digestibility, utilizing in situ and in vitro approach in mature Hereford cattle. Heating to 110°C for 10 min resulted in decreased ruminal degradability of dry matter and crude protein relative to a non-heated control, and resulted in greater intestinal crude protein digestibility than when heated to 120°C. In the second study, 28 Holstein bull calves were used in 2 × 2 factorial design, to assess the effect of CM heat-treatment and glycerol supplementation on calf performance and on GIT development at weaning. The interactions between the main effects were minimal. Canola meal heat-treatment negatively affected calf performance, by decreased starter intake, average daily gain (ADG), final body weight, and GIT development with lighter ruminal and jejunal tissue weights. Heat-treatment did not impact gene expression of short-chain fatty acids (SCFA), peptide and amino acid transporters that were investigated in GIT, nor the activity of brush border enzymes in the small intestine. Glycerol inclusion in the starters increased starter intake and ADG. Additionally, when calves were fed starters with glycerol, the concentration of ruminal SCFA increased and jejunal tissue weight was greater, although no changes were observed for indicators of ruminal development. Glycerol downregulated the expression of MCT1 in ruminal epithelium and upregulated it in proximal jejunal epithelium. Glycerol also increased activity of dipeptidylpeptidase IV in middle jejunum. Third and fourth study assessed the effect of different protein sources, either CM or soybean meal (SBM), as well as microencapsulated sodium butyrate (MSB) inclusion in 2 × 2 factorial design. Third study utilized bull calves and fourth study utilized heifer calves to assess starter intake and growth. Additionally, bull calves were also used for the assessment of GIT development. Few interactions between the treatments were present. Canola meal as protein source did not have the same effect across both studies in terms of performance. For bull calves, CM resulted in decreased pre-weaning starter intake, and ADG and feed efficiency during the weaning phase. Additionally, dry matter digestibility was decreased when CM was used. For heifer calves, CM inclusion increased starter intake without differences in ADG and feed efficiency. Across both studies, CM inclusion resulted in decreased fecal score, indicating lesser severity of diarrhea. Supplementation of MSB increased pre-weaning starter intake; however, it did not affect growth of calves. Canola meal inclusion did not impact the molar proportions of major SCFA in ruminal fluid, but increased jejunal weight and length. Canola meal use in the starters tended to increase abomasal weight and upregulated MCT4 and GPR43 expression in the abomasum. While CM did not impact activity of brush border enzymes, CM downregulated expression of PEPT2 in proximal jejunum and ATB0+ in ileum. Microencapsulated sodium butyrate decreased the length of ruminal papillae, as well as ruminal epithelial surface area. Additionally, omasal epithelial layers were smaller when MSB was supplemented. When MSB was included in starters, no changes were detected for GIT organ weights. Expression of MCT1 was upregulated in the ruminal epithelium with MSB supplementation. Microencapsulated sodium butyrate also increased activity of aminopeptidase enzymes in duodenum and ileum. In the final study, the multiple levels (0, 15, 30, 45 and 60% CP) of partial replacement of SBM with CM were investigated using Holstein heifer calves in order to assess starter intake, growth, ruminal fermentation, and digestibility. Linearly increasing CM inclusion in the starters decreased starter intake and crude protein digestibility, but did not affect calf growth. The molar proportion of ruminal propionate increased with increasing CM inclusion, whereas acetate decreased. In conclusion, the partial replacement of SBM with CM can help mitigate the decrease in ADG observed when full replacement of SBM is used, although decreased starter intake may still occur. The use of heat-treated CM, when compared with non-heated CM, decreased starter intake and growth of the calves, and compromised the development of the GIT. To improve calf performance and GIT development, glycerol can be included in the starter at 5% DM. Supplementation of MSB in starters may negatively affect the development of the rumen and omasum. In general, partial replacement of SBM with CM can be reasonably used to ensure adequate protein supply from solid feed in dairy calves.
protein source, solid feed
Doctor of Philosophy (Ph.D.)
Animal and Poultry Science