Metabolism of Recently Weaned Dairy Calves Utilizing Various Forage and Fiber Feeding Systems
Open Access
- Author:
- Mitchell, Lucas
- Graduate Program:
- Animal Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 03, 2020
- Committee Members:
- Arlyn Judson Heinrichs, Dissertation Advisor/Co-Advisor
Arlyn Judson Heinrichs, Committee Chair/Co-Chair
Tara Louise Felix, Committee Member
Kevin John Harvatine, Committee Member
Marvin H Hall, Outside Member
Terry D Etherton, Program Head/Chair - Keywords:
- Weaned calf
forage
digestibility
growth - Abstract:
- Forage provision may be beneficial to growth and intake of pre-weaned calves that are offered concentrates that are highly processed (pelleted or finely ground). However, forage provision for pre-weaned calves offered minimally processed concentrates may negatively impact growth and intake, which would slow rumen development. As a result, it is the best practice to withhold forage from calves offered minimally processed concentrates until after weaning. This allows calves to have enhanced rumen development which would, in turn, allow them to more fully digest, and make better use of, forage within the ration. However, the rumen of the recently weaned calf is still developing, especially in terms of volume, which makes them susceptible to gut fill limitations on intake. This is important to consider as most research studies evaluating various forage and fiber feeding systems for calves have only tracked them for 2 to 3 wk after weaning. There are few data that have focused exclusively on the ability of recently weaned calves from 7 to 16 wk of age to utilize various forage and fiber feeding systems. The objective of this dissertation was to evaluate the metabolism of recently weaned dairy calves utilizing various forage and fiber feeding systems. In the first study, the objective was to determine the effects of converting calves from a component-fed ration to a total mixed ration (TMR) at 8, 10, or 12 wk of age on intake, growth, and nutrient digestibility. Holstein calves (n = 40) were randomly assigned to 1 of 4 groups (no TMR, TMR conversion at 8, 10 or 12 wk; T0, T8, T10, and T12, respectively). Calves were weaned at 6 wk of age and housed individually. Data were collected from 7 to 14 wk of age. Rations, consisting of a 20% crude protein texturized starter and grass hay, were offered ad libitum as separate components or as a TMR with 85% starter and 15% grass hay on a dry matter (DM) basis. Intake tended to be reduced for calves converted to TMR earlier. However, calves fed TMR consumed more hay and less starter than those that were component fed. The differences in composition of the feed consumed led to calves fed T8 consuming the least amount of metabolizable energy. This further led to calves fed T8 tending to have the least average daily gain (ADG), final body weight (BW), and hip growth and significantly less empty BW gain and final hip width compared to calves fed T0. Feed efficiency was not different between the groups. Digestibility of neutral detergent fiber (NDF) and acid detergent fiber (ADF) was increased for calves offered TMR at 9, 11, and 13 wk of age. Rumen pH was increased when calves were fed a TMR. In the second study, the objective was to determine effects of various forages and live yeast culture on intake, growth, nutrient digestibility, and ruminal fermentation of weaned dairy calves. Holstein calves (n = 45) were randomly assigned to 2 × 3 factorial treatments: live yeast culture (Y; Yea-Sacc, Alltech, Inc.) or no yeast (NY); and alfalfa haylage (AH), corn silage (CS), or grass hay (GH). Calves were weaned at 6 wk of age and housed individually. Data were collected from 7 to 16 wk of age. Diets, consisting of an 18% crude protein texturized grower (Y or NY) and assigned forage, were offered as separate components until 9 wk of age. After 9 wk, diets were offered as a TMR. Concentrate intake was capped at 2.25 kg of DM/d, while forage was offered ad libitum. Calves were fed TMR to limit concentrate intake, and additional forage was offered ad libitum after 8 h if the entire TMR allotment was consumed. The TMR contained equal NDF concentration from forage (8 0.5%) on a DM basis for each diet. Metabolizable energy and DM intake was least for calves consuming GH. Forage intake relative to DM intake increased as calves aged (AH = 20.0 to 44.4%, CS = 24.5 to 37.6%, GH = 11.3 to 32.3% at 10 and 16 wk of age respectively). Calves fed CS had the greatest ADG and empty BW gain, while calves fed GH had the least. Because of this calves offered GH tended to have the least final BW. Despite differences in weight gain, there were no differences in structural growth. Digestibility of NDF and ADF was least for calves fed CS, while starch digestibility was least for calves fed AH. Mean and minimum ruminal pH increased with age. VFA profile was altered by treatment such that calves fed CS had the least proportion of acetate and greatest proportion of propionate, while calves fed AH had the greatest proportion of butyrate. Yeast did not impact intake, growth, or ruminal pH. However, there was an interaction between yeast and forage on VFA profile. In the third study, the objective was to determine effects of increasing GH inclusion level on weaned dairy calf growth, intake, digestibility, and rumen fermentation. Holstein calves (n = 45) were randomly assigned to 1 of 3 TMR with increasing GH (10%, 17.5%, or 25% on a DM basis; LGH, MGH, or HGH respectively). Calves were weaned at 6 wk of age and housed individually. Data were collected from 7 to 16 wk of age. Diets, consisting of texturized calf starter (20% crude protein) and coarsely chopped GH, were offered ad libitum as separate components from 7 to 9 wk of age. After 9 wk, feed was offered as a TMR containing the assigned level of GH and fed according to the clean bunk feeding strategy, where feed is offered in a manner to accomplish near ad libitum intakes while limiting refusals. Feeding increased levels of GH resulted in a linear decline in final BW, ADG, DM intake, and metabolizable energy intake. Plasma β-hydroxybutyric acid tended to decline with increased GH. Although there were no differences in DM or starch digestibility, NDF and ADF digestibility increased linearly with increased GH. There were no differences in mean ruminal pH or total VFA, but there was an interaction between GH level and time indicating that calves offered 17.5 and 25% GH had different feeding behavior than those offered 10% GH. In the fourth study, the objective of was to determine the effects of replacing soybean hull (SBH) pellets with grass hay (GH) on growth, intake, total tract digestibility, and ruminal microbial nitrogen production of weaned dairy calves from 8 to 16 weeks of age. Holstein calves (n=16) were randomly assigned to 1 of 4 rations containing, on a DM basis, 76% grower with the remaining 24% being made up of different amounts of SBH pellets and GH [0% GH and 24% SBH (0GH), 8% GH and 16% SBH (8GH), 16% GH and 8% SBH (16GH), or 24% GH and 0% SBH (24GH)]. Calves were weaned at 6 wk and housed individually. Data were collected from 8 to 16 wk of age. From 8 to 9 wk of age calves were offered a ration of 50% of texturized starter (20% CP and 35% starch) and 50% of their assigned diet. From 9 wk until the end of the study, calves were offered 100% of their assigned diet. Calves fed 0GH and 8GH had a 20% increase in DM intake, ADG, and feed efficiency compared to calves fed 16GH and 24GH. Calves offered 8GH had the greatest NDF and ADF digestibility as well as the greatest estimated microbial N yields. Feeding increasing inclusions of forage increased rumination time (2.75, 6.89, 7.18, and 8.16 h/d for 0GH, 8GH, 16GH, and 24GH) and decreased fecal geometric mean particle size by ~35% compared to calves offered 0GH. In summary, feeding calves to a TMR increases hay consumption and subsequently decreases starter and total DM intake. This tends to reduce weight and structural growth (although calves fed a TMR as early as 8 wk of age still accomplished ADG exceeding 1 kg/d). Furthermore, feeding calves a TMR increased ruminal pH and fiber digestibility, which may have allowed calves to be fed a 15% grass hay TMR as early as 8 wk and still achieve desirable growth goals. Feeding calves GH reduced weight gain compared to calves fed AH or CS, but growth rates of calves were sufficient for them to meet future growth goals for breeding and freshening regardless of forage provided. Furthermore, weaned calves are capable of consuming greater amounts of forage while still maintaining acceptable growth rates than previously thought. Feeding calves more than 10% GH will reduce growth and intake and alter rumen digestibility prior to 16 wk of age. Furthermore, feeding behavior may be altered at some point between feeding 10 and 17.5% GH. Replacing up to 8% of SBH with GH is beneficial to weaned calf performance. Diets containing 8% coarse GH and 16% SBH improved rumen functionality and allowed calves to extract a greater amount of energy from their ration and exhibit improved feed efficiency compared to calves offered other levels of coarse GH and SBH.