Investigating dietary methods for improving fatty acid digestibility and milk fat yields in lactating dairy cattle
Restricted (Penn State Only)
- Author:
- Burtnett, Sarah
- Graduate Program:
- Animal Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 19, 2024
- Committee Members:
- Ramesh Ramachandran, Program Head/Chair
Robert Vansaun, Outside Unit & Field Member
Tara Felix, Major Field Member
Arlyn Heinrichs, Major Field Member
Kevin Harvatine, Chair & Dissertation Advisor - Keywords:
- milk fat depression
emulsifiers
oleic acid - Abstract:
- Energy is a limiting factor for milk production in lactating dairy cows and fat supplementation is often used to raise dietary energy content. There are two common methods for increasing the fatty acid (FA) content of the diet; oilseeds and fat supplements, though both present challenges. The inclusion of oilseeds, such as soybeans, can raise the fat content of the basal diet and are generally a cost-effective means for doing so. However, fat provided by conventional oilseeds introduces more unsaturated fatty acids (UFA), primarily linoleic (18:2), into the rumen and increases the risk for biohydrogenation (BH)-induced milk fat depression (MFD) through alterations in microbial pathways within the rumen. This ultimately leads to a decrease in fat content and value of milk. Prilled fat supplements are a common method to supplement FA and are high in saturated fatty acids (SFA), predominantly palmitic (16:0) and stearic (18:0), with low levels of oleic acids (cis-9 18:1) and little to no polyunsaturated FA. While these SFA supplements do not increase the risk of BH-induced MFD, they vary greatly in FA profile, which may explain the large variation in FA digestibility reported in the literature. Poor digestibility of SFA supplements could be due to a lack of endogenous emulsifying capacity within the small intestine. The overarching objective of this dissertation was to examine methods to increase milk fat production in lactating dairy cows by reducing the risk of BH-induced MFD and increasing FA digestibility. The mitigation of MFD was the focus of two studies. First, the methionine analog 2-hydroxy-4-methylthiobutanate (HMTBa) blended into a saturated FA prill was tested due to previous work indicating that HMTBa blended with corn grain reduced BH-induced MFD. The hypothesis was that blending HMTBa with the SFA prill would reduce MFD and improve FA digestibility. Fifteen multiparous cows in a 3 x 3 Latin square design were fed HMTBa at 0, 12.5, and 25 g per day within the SFA prill. A diet with a moderate-risk of MFD (29.3% NDF, 0.75% soy oil) was fed for 18 d followed by a higher-risk diet (28.5% NDF, 1.5% soy oil) diet for 3 d. Feeding HMTBa blended with saturated FA did not alter performance or change response when diet starch and unsaturated FA were increased, although this challenge diet failed to increase trans-10 18:1 in milk fat limiting interpretation of the interaction with BH-induced MFD. In the second study, a high oleic expeller soybean meal was compared to expeller meal from conventional soybeans. The hypothesis was that the higher oleic acid (cis-9 18:1) and lower linoleic acid (18:2 n-6) would decrease the risk of BH-induced MFD and improve FA digestion. Eighteen multiparous cows were fed treatments in a crossover design. Either a control expeller soybean meal or a high oleic soybean expeller meal were fed at 7.5% of DM and there were two phases with a basal diet with lower-risk of MFD (33% NDF, no oil) fed for 14 d and moderate-risk for MFD (28.9% NDF, 0.5% corn oil) fed for the last 10 d to test an interaction with BH-induced MFD. The moderate risk diet successfully caused BH-induced MFD, though the HO soybean expeller meal did not reduce the severity of MFD or alter milk production compared to the conventional soybean expeller meal. Overall, the experiment demonstrated that high oleic acid soybean expeller meal can serve as a suitable replacement for conventional soybean expeller meal, although the benefits for MFD may not be observable in lower-fat ingredients like expeller soybean meal compared to full-fat soybeans. The final two studies focused on potential methods to increase digestibility of FA prills by increasing emulsifying capacity in the small intestine. Oleic acid acts as an emulsifier due to its amphiphilic properties and palmitic acid often varies in FA prills. Prills higher in palmitic acid have been reported to have higher digestibility. In the third study of this dissertation, 8 primiparous and 8 multiparous cows in a 4 x 4 Latin square design were fed either a low-fat control diet or diets that contained a control SFA prill, a SFA prill high in oleic acid, or a SFA prill high in palmitic acid. The hypothesis was that increasing PA will increase milk fat yield and increasing cis-9 18:1 will increase FA digestibility and milk yield. Increasing cis-9 18:1 within the FA prill increased milk and milk fat yield. The parity of cows interacted with treatment on both milk yield and dry matter digestibility measurements indicating that age and production level of cows may influence digestibility and the ability to incorporate energy from a FA prill into milk. The final study compared the effect of emulsifying compounds blended in a saturated FA prill on milk production and FA digestion. Fifteen cows in a 5 x 5 Latin square were used to test the effect of the addition of either saturated FA prill that contained magnesium-reacted oleic acid, lysolecithin, polysorbate, or monoglyceride compared to FA prills with no exogenous emulsifying compound. The hypothesis was that the addition of an emulsifier would increase FA digestibility and support higher milk fat yield. Polysorbate increased FA digestibility indicating potential for exogenous emulsifiers, though this change did not translate into increased milk production. In conclusion, this dissertation expands on the current understanding of methods for improving milk fat yield via two mechanisms. In the first two experiments, methods for mitigating BH-induced MFD were studied to prevent loss of milk fat. All four experiments were focused on methods for increasing the digestibility of dietary FA to increase FA substrate for milk fat synthesis.