The individual and interactive effects of rumen modifiers on feed efficiency in lactating dairy cows
Date
2024-08
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Rigert, Sydney
Major Professor
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Appuhamy Jayasooriya, Ranga
Baumgard, Lance H
Carpenter, Gail
Koltes, James E
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Abstract
The Food and Agriculture Organization 2023 publications highlight that increasing the productivity of global livestock systems through improved feeding, genetics, and husbandry practices is essential to make them sustainable. This goal is, however, not new to the US dairy industry, given the tremendous productivity improvements achieved through continuous advancements in genetics, nutrition, and management practices over the last century. The US dairy industry continues to become more sustainable through nutritional advancement. Improving the feed efficiency of lactating cows (e.g., fluid milk volume per unit feed weight) garners the utmost priority, given the increasing feed prices and the carbon footprint associated with feed crop production. Being a ruminant animal, the feed efficiency of dairy cows largely depends on rumen microbiota and their functions, such as carbohydrate fermentation and the efficiency of microbial protein synthesis. Ionophores, predominantly monensin, are widely used in US dairy operations to enhance the feed efficiency of cows, in addition to other purposes, such as bloat and ketosis prevention. Ionophores are classified under a special feed additive category termed rumen modifiers because they modulate rumen microbiota composition and thus shift the fermentation, leading to increased feed efficiency attributed to increased milk yields, decreased feed intake, or both. However, feeding monensin can elicit milk fat depression and elevated milk urea nitrogen, depending on feeding conditions. The European Union has restricted monensin use in dairy cows, prompting a need to develop other strategies to improve feed efficiency. In that regard, feed additives with a “natural” outlook, for instance, direct-fed microorganisms or their fermentation extracts and secondary plant metabolites, have been proposed. The preliminary findings, predominantly from in vitro investigations, demonstrate these novel feed additives may modulate the rumen function through both non-competitive and competitive mechanisms to that of monensin. Given that most dairy cows are given monensin, and monensin can considerably increase the income over feed cost ($0.29 to 0.42 per cow/d) in US dairy operations, it is crucial to evaluate these novel rumen modifiers for their ability to modulate cow productivity and feed efficiency against monensin.
Chapter 2 of this thesis covers an experiment designed to evaluate the individual and interaction effects of a fermentation extract derived from Bacillus licheniformis (BLFE) and monensin (Rumensin®; R) on production performance and feed efficiency of lactating dairy cows fed a corn silage-based TMR. This 90-d study utilized 20 primiparous and 40 multiparous Holstein cows at 108 ± 35 DIM when the study began. Cows were assigned randomly to two monensin [0 and 420 mg/cow/day] and two BLFE [0 and 2.4 g/cow/day] doses in a 2 × 2 factorial arrangement. The study consisted of four consecutive periods starting with training (13 d) and baseline measurement (14 d) periods, where cows received the basal TMR containing monensin, followed by treatment adaptation (21 d) and response measurement (42 d) periods, where cows received the treatment doses of monensin and BLFE top-dressed on the basal TMR devoid of monensin. Individual and interaction effects of monensin and BLFE on DMI, milk production parameters, multiple feed and nutrient utilization efficiency matrices, and body measurements were analyzed with a mixed-effect model accounting for the repeated measures and baseline measurement variability. Additionally, treatment effects on volatile fatty acid concentrations and molar percentages in rumen fluid obtained with an oral stomach tube and feces, apparent total tract digestibility of nutrients, and blood amino acid concentrations were analyzed. Monensin did not affect the milk yield or gross feed efficiency (milk yield: DMI), but it increased milk fat yield (0.10 kg/d), fat-corrected (FCM), energy-corrected (ECM), and solids-corrected (SCM) milk yields by 2.06, 1.92, and 1.83, respectively (P = 0.02). BLFE increased milk protein content by 0.06 percentage units (P = 0.01), irrespective of whether the diet contained monensin or not. However, BLFE tended to increase milk yield (0.98 kg/d; P = 0.07), and increased gross feed efficiency, dietary protein utilization efficiency, and average daily gain, only in the absence of monensin in the diet (P < 0.05). BLFE also increased serum total concentrations of both essential and non-essential amino acids only in the absence of monensin in the diet. Despite the blood amino acid concentrations reflecting an increased metabolizable protein supply, BLFE decreased apparent total tract CP digestibility in the absence of monensin, and monensin attenuated that digestibility reduction (P = 0.04). Monensin or BLFE did not affect acetate or propionate concentrations in rumen fluid but tended to interactively modify the fecal concentrations (P < 0.10), indicating that rumen modifiers can affect hindgut microbiota function, which can lead to perturbed apparent total tract digestibility estimates. Overall, this study data supported the potential of BLFE to improve the feed efficiency of lactating dairy cows, particularly when added to diets without monensin. Additionally, they support the potential of monensin to increase milk fat yield under some feeding conditions.
Furthering the investigations into the interactive effects of novel rumen modifiers and monensin, the experiment described in Chapter 3 was designed to determine the effects of feeding a blend of secondary plant metabolites, such as cinnamaldehyde and garlic oil (NECGO) alone or with monensin in lactating dairy cows. In this study, 20 primiparous and 40 multiparous Holstein cows (81 ± 29 DIM) were assigned to treatments in a 2 × 2 factorial arrangement, with monensin [0 and 406 mg/cow/day] and NECGO [N; 0 and 710 mg/cow/day] doses (n = 15 cows/treatment). In alignment with the previous study, cows received the basal TMR containing monensin in the training (10 d) and baseline measurement (10 d) periods. Monensin was removed from the TMR, and the treatment doses were top-dressed on the TMR devoid of monensin during the adaptation (21 d) and measurement (49 d) periods. The same production and efficiency responses of the previous study were measured in this study, and milk fatty acid composition was an additional response variable of interest. Treatment effects were analyzed with the same procedure used in the previous study. The results indicated a milk yield increase (1.2 kg/d; P = 0.01) that did not change gross feed efficiency or DMI in response to feeding monensin. Monensin increased milk fat yield (0.1 kg/d; P = 0.04) and FCM, ECM, and SCM by 2.6, 2.3, and 2.1 kg/d, respectively (P < 0.05). The increase in milk fat yield in response to monensin was associated with increased palmitate concentration in milk fat (P = 0.02). NECGO decreased DMI by 1.9 kg/d (P = 0.02) and increased gross feed efficiency by 8% (P < 0.01) without affecting milk yield in the absence of monensin. Independent of monensin, NECGO increased milk fat content by 0.3 percentage units (P < 0.01) but did not increase the milk fat yield, because of the unchanged milk yield. The increased milk fat content by NECGO was associated with increased saturated and preformed fatty acids concentrations (P < 0.05). NECGO increased milk protein efficiency (P = 0.03), again in the absence of monensin. In conclusion, the findings of both studies highlight the potential of the novel feed additives to improve feed efficiency by increasing milk yield or decreasing DMI when fed without monensin. Those feed additives may also improve dietary crude protein utilization efficiencies, implying positive implications for economic and environmental sustainability. A comprehensive cost-benefit analysis would help draw robust conclusions on their economic advantage against monensin.
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