FACTORS THAT AFFECT RUMEN FERMENTATION AND TOTAL TRACT DIGESTION IN PRECISION FEEDING DAIRY HEIFERS
Open Access
- Author:
- Pino San Martin, Felipe Humberto
- Graduate Program:
- Animal Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 24, 2016
- Committee Members:
- Arlyn Judson Heinrichs, Dissertation Advisor/Co-Advisor
Arlyn Judson Heinrichs, Committee Chair/Co-Chair
Chad Daniel Dechow, Committee Member
Kevin John Harvatine, Committee Member
Gregory Wayne Roth, Outside Member - Keywords:
- Heifers
precision feeding
starch
passage rate
digestibility
rumen fermentation - Abstract:
- In the last decade farmers and researchers have focused on nutritional methods and management to improve feed efficiency in rearing dairy heifers. Precision feeding has been an interesting alternative to traditional ad-libitum, high forage diets fed to heifers. Precision feeding is an economical way to raise heifers that modifies physiological and nutritional responses, making heifers more efficient without affecting growth, first lactation milk production, or the animal in any way that we are aware. The literature available has provided information about dietary crude protein, optimal N intake, and diet forage-to-concentrate ratio (F:C) in precision feeding, but still more information is necessary. In the present dissertation, three experiments were conducted to evaluate the effect of starch, neutral detergent fiber (NDF) source, fiber digestibility, and rate of passage in precision feeding dairy heifers. The first experiment had two objectives: evaluate effects of starch concentration on digestibility and rumen fermentation and compare two sources of trace minerals (TM; inorganic, ITM, and organic, OTM, form) on digestibility and rumen fermentation. Eight rumen cannulated dairy heifers (15.4 ± 0.8 mo of age and 438.31 ± 18.08 kg of body weight) were subject to a split-plot, 4 × 4 Latin Square design with 19-d periods; 15 d adaptation and 4 d sampling. The whole-plot factor was type of TM; organic as proteinates (OTM) or inorganic sulfates (ITM), and the subplot was starch level (3.5, 12.9, 22.3, and 31.7%). Results of this experiment supported the hypothesis that the type of TM affects rumen bacteria populations and produces responses in ruminal fermentation. Digestibility of dry matter (DM), NDF, acid detergent fiber (ADF), hemicellulose, and starch was not affected by treatments. The OTM decreased rumen pH and increased total volatile fatty acid (VFA) production and butyrate concentration. This can be explained by the lower time consuming the ration with OTM, which led to a faster fermentation. Also we hypothesize as the higher bioavailability of OTM suggests a faster utilization of the TM and accelerated replication of ruminal micro-organisms, stimulating ruminal fermentation and VFA production. Butyrate was also linearly increased as starch level increased. In general, TM excretion was not affected by type of TM. Plasma TM concentration was not different by treatment except for Mn, which was higher for OTM. However, mineral intake was reduced in OTM, but blood concentration was not different between TM types. These results suggest that OTM have higher TM absorption compared with the ITM. On the other hand, urine and total manure excretion were higher for ITM, suggesting that ITM stimulated water intake and produce more manure. In summary, the type of TM affected rumen fermentation such that OTM was absorbed to a greater extent than ITM, suggesting higher bioavailability for this form of TM. The objective of the second experiment was to evaluate sorghum silage (SS), including digestibility and fermentation parameters, in precision-fed dairy heifers. Eight Holstein heifers (13.7 ± 0.6 mo of age and 364.8 ± 17.64 kg of body weight) fitted with rumen cannulas were used in a replicated 4 × 4 Latin Square design; treatments were 4 levels of F:C (85:15, 75:25, 65:35, 55:45). When the concentrate proportion of the diet increased, heifers tended to improve feed efficiency, primarily due to lower DM intake (DMI) with the same average daily gain (ADG) over diets with a high proportion of forage. Rumen pH was affected by F:C, decreasing as the proportion of concentrate increased in the diet since heifers spent less time consuming feed. However, pH was never lower than 5.7 in diets with F:C 55:45, and fiber digestibility was not affected. Volatile fatty acid proportion was slightly influenced by treatment, where butyrate increased as concentrate increased in the diet. Dry matter and starch digestibility were affected by F:C and were improved in diets with more concentrate. Neutral detergent fiber, ADF, and hemicellulose digestibility were not affected by F:C. Wet and dry feces were reduced linearly as F:C decreased, but total manure was not affected by treatment due to increased urine production on high concentrate diets. In the in situ analysis, corn silage had a faster rate of digestion for DM and NDF than SS. This result suggests that the overall digestion of SS was diminished, probably because of the high NDF. Brown mid-rib SS can effectively be fed in precision diets for dairy heifers. Specifically in this study, the 65:35 F:C presented better performance based on rumen fermentation, VFA, rumen pH, digestibility, and feed efficiency. The third experiment was conducted with the objective to compare ad-libitum vs. precision feeding diets with two forages and different levels of NDF to evaluate rumen fermentation, diet digestibility, feed efficiency, and digesta passage rate. Eight Holstein heifers (18.4 ± 0.6 mo and 457.2 ± 27.29 kg BW) fitted with rumen cannulas were used in a two-factor, split-plot, Latin Square design with 19-d periods, 14 d of adaptation and 5 d of sampling. The whole-plot factor was feeding system with ad-libitum or precision feeding and 4 heifers in each plot. The subplot included 2 factors: forage quality (low quality: grass hay, LFQ; high quality: corn silage, HFQ) and NDF content (high NDF, 48 % HNDF; low NDF, 39.8 %, LNDF). In this study we showed that the reduction in DMI for precision feeding diets improved feed efficiency in comparison with ad-libitum diets for dairy heifers. We observed that HFQ diets increased DMI, resulting in altered feed efficiency due to changes in intake based on fiber intake. Precision-fed diets resulted in a lower minimum rumen pH than ad-libitum diets, but the amount of time spent at the minimum pH was not great enough to reduce fiber digestion or rumen fermentation. Ad-libitum diets resulted in lower mean pH than precision-fed diets, but the rumen pH was more consistent throughout the day than in precision feeding, where rapid fermentation resulted when heifers ate much of their daily diet within a small amount of time. This effect was stronger when corn silage was the forage component of the diet. Also, we observed that HNDF diets presented higher minimum pH, suggesting that the presence of additional fiber stimulates rumination and buffers the rumen. Overall, VFA proportions were not affected by the type of diet but were clearly modified by forage quality, where grass hay diets had higher proportions of acetate and corn silage diets higher proportions of propionate. Overall, apparent total tract digestibility was not affected by the type of diet; however, DM digestibility increased with HFQ and decreased with HNDF level. In situ digestibility was affected by forage quality and NDF level, where grass hay diets resulted in a greater 48 h rumen degradation than corn silage. Rate of passage was not affected by type of diet 22 h after feeding, but it was highly affected with the rumen at maximum capacity, 3 to 4 h after feeding. In this study, ad-libitum diets had higher passage rate than precision diets for the nutrients analyzed. Rate of digestion was affected by forage quality in the post-feeding evaluation, indicating that corn silage diets had higher digestion rates than grass hay diets. This suggests that higher amounts of indigestible NDF reduced the digestion capacity of the rumen. With the results obtained in this study, we can state that the retention time for precision-fed diets was higher than ad-libitum diets and could lead an increased rumen digestion of nutrients. Also, grass hay diets had a higher retention time compared to corn silage diets. This effect was more significant in the precision-fed heifers. In addition, fluid dilution rate was higher for the ad-libitum diets. Grass hay diets presented a higher fluid dilution rate than corn silage-based diets. In summary, the three factors analyzed in this study affect ruminal fermentation, rumen pH, nutrient digestion, and rate of passage, but the most important result was the difference in feed efficiency presented in the precision feeding diets that could lead to a reduction in the cost of raising dairy heifers.