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Objectives of this research were to characterize residual feed intake (RFI) in growing and finishing steers and examine phenotypic correlations between performance, feed efficiency, carcass, digestib ility, and physiological indicator traits. The research included two growing studies and one finishing study. Braunvieh-sired crossbred steers (n = 169) and Santa Gertrudis steers (n = 120) were individually fed a roughage-based diet for 77 d during the growing phase. Santa Gertrudis steers (n = 120) were individually fed a grain-based diet for 80 d during the finishing phase. Individual body weight (BW) and feed intake data were recorded. Residual feed intake was calculated as the difference between actual dry matter intake (DMI) and DMI predicted from linear regression of DMI on mid-test metabolic BW. During the growing phase, initial ultrasound measures of 12th rib fat thickness (FT) and final ultrasound measures of Longissimus muscle area (LMA), FT, and intramuscular fat (IMF) were obtained. During the finishing phase, initial and final LMA, FT, and IMF ultrasound measurements were obtained. Finishing steers were slaughtered at 1.0 cm of FT and carcass cooler traits measured. Blood samples were collected at the start and end of each feeding period and analyzed for physiological indicators. Temperament traits were also measured at the start and end of each feeding period. Growing and finishing steers with low RFI consumed 19-22% less feed than growing and finishing steers with high RFI, but did not differ in average daily gain (ADG). Consequently, steers with low RFI were also more efficient as measured by feed conversion ratio and partial efficiency of growth. Steers with low RFI had less FT compared to steers with high RFI. Initial serum IGF-I was correlated with RFI in growing steers indicating that IGF-I could be a potential indicator trait for RFI in growing cattle. Additionally, RFI was correlated with digestibility to indicate more efficient cattle had higher dry matter digestibility. Results indicate that RFI has potential to allow producers to select more efficient animals without increasing growth rate. Moreover, serum IGF-I may facilitate early detection and more accurate selection of animals that are superior for growing RFI.

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The overall objective of this thesis was to assess the effect of feed area design including feeding space availability, barrier type and stocking density, on the feeding behaviour of dairy cows. Feed intake in dairy cows is directly related to milk production, thus a good food supply is extremely important to the modern, high producing dairy cow. Intake is critical for improving milk production, health, body condition and the welfare of the animals. Feeding designs can have a major effect on behaviour and feed intake, therefore it is an important consideration when housing cattle and other livestock. The effect of altering the amount of space allowance available at the feed-face highlighted a significant effect on feeding patterns. As the space allowance increased the number of feeding bouts also increased (P<0.001) and length of bouts decreased (P<0.05). However, when provided with extra space at the feed-face, cows did not increase their feed intake as hypothesised, possibly as a result of the differences between individual animals being masked by an overall group effect. The number of aggressive interactions decreased as the space allowance increased (P<0.001) and furthermore, the number of times individuals were displaced from the feeding area also decreased as the space allowance increased (P<0.05). Subsequently, preference tests were used as a behavioural tool to determine how individual cows perceive their feeding environment with specific emphasis on understanding what difficulties low ranking animals face at the feed-face. Subordinate cows showed a significant preference for feeding alone rather than next to a dominant when they were offered high quality feed on both sides of a Y-maze test (P<0.001). When “asked” to trade-off between feed quality and proximity to a dominant cow, subordinate cows chose to feed alone on low quality food. A follow-on experiment using the same methodology was undertaken and aimed to identify the space allowances at which cows would not trade-off food quality. Four different space allowances were tested. At the two smaller space allowances, cows preferred to feed alone and for the two larger space allowances, cows had no significant preferences. The feed barrier has been shown to have a major effect on feeding and social behaviour of group housed dairy cows. A barrier design that provides some sort of separation between cows has also been shown to reduce competition. The aim of the final study was to determine if a feed barrier which obscured the cows’ visual field whilst feeding would increase vigilance behaviour and alter normal feeding behaviour, particularly for subordinates. Two different types of feed barrier were tested at four different stocking densities. The average daily feeding time was higher when cows were fed using a conventional headlock system compared to an electronic feeding system (P<0.05). All groups of cows displayed vigilance scans, however, neither type of barrier, feed space allowance, or dominance rank had an effect on the frequency of scans. These results indicate that neither feeder design nor stocking rate affect vigilance in dairy cows, at least over the treatment conditions assessed in the current study. The results of this research illustrate that to achieve the maximum levels of feeding behaviour and a reduction of aggressive behaviour, the cows’ environment must be such that it provides sufficient space and feed barrier design which will allow normal social behaviour. Over-stocking at the feed-face should be avoided to reduce competition. Future research should consider the long term effects of over stocking and competition on dry matter intake (DMI), milk production and health.

Bibliography: leaves 175-196. The influence of starch in grain-based diets on fat development in cattle and sheep is investigated.

Graduation date: 1998

Two studies were conducted to determine the effects of zinc (Zn), copper (Cu) and/or selenium (Se) on the humoral immune response of weaned steers fed diets deficient in these minerals. Steers were bled weekly for eight weeks to measure plasma mineral levels. Humoral immune response was measured as antibody response to Keyhole limpet hemocyanin (KLH) over seven weeks of the trials. Steers were injected with 0.5 ml KLH vaccine on weeks 2 and 5 of the Zn study. Ten steers (5 per treatment) were randomly assigned to either a Zn supplemented (z), 3.25 ml injectable zinc-oxide suspension (100 mg/ml oil) or a control (c) treatment. Plasma Zn was maintained at higher (P<.05) levels in supplemented steers from week 3 through week 8. Humoral immune response was not different (P>.10) between treatments. In 1988, 20 steers were stratified by weaning weight and randomly assigned to one of four treatments: 1) Injectable Se 1 ml Mu-Se/ 90.9 kg body weight, 2) Injectable Molycu 2 ml, 3) control, or 4) Se + Cu. Plasma Cu was higher (P<.05) in treatments 2 and 4 from week 2 through 8. Steers were injected with 0.5 ml of KLH vaccine on weeks 2 and 6. Immune response was not different (P>.10) between Cu supplemented steers and other treatments. Plasma Se was higher (P<.05) in treatment 1 as compared to 2 and 3, but not different (P>.10) from 4. Immune response was highest (P<.05) in treatment 1 with others not different(P>.10). In 1990, a second trial was conducted with 48 steers stratified by weight and randomly assigned to one of the same four treatments. Plasma Cu was higher (P<.05) on week 3 for both groups receiving Cu. Plasma Se was higher (P<.05) on weeks 2 through 5 for both groups receiving Se. Humoral immune response was higher (P<.05) on weeks 7 and 8 for both groups receiving Se. Humoral immune response was uneffected by Zn status of weaned beef steers. Selenium had a positive effect and Cu had no effect on humoral immune response of weaned beef steers. Copper also tended (P=.07) to reduce the positive response from Se. / Graduation date: 1991

Two experiments were conducted to investigate the effects of metabolic acid-base balance on feed intake and susceptibility of dairy heifers to ketoacidosis. Animals were fed two dietary cation-anion difference diets [dietary cation-anion difference is defined as mEq (Na++K+)-(Cl -+S2-) kg-1 dietary dry matter], a high dietary cation-anion difference (positive) and a low dietary cation-anion difference (negative). The heifers fed the positive dietary cation-anion difference had significantly higher blood pH, blood bicarbonate and dry matter intake than heifers fed the negative dietary cation-anion difference. There was an initial decrease in dry matter intake by the heifers fed the negative dietary cation-anion difference. However this difference was not significant by the end of the two week period. It is unclear whether the reduced dry matter intake in the heifers fed the negative dietary cation-anion difference is the result of metabolic-acidosis caused by the anionic salts, poor palatability of the anionic salts or a combination of both. Heifers were induced into a nervous ketosis by feeding 1,3-butanediol. There was no difference in the incidence of ketosis between animals fed positive and negative dietary cation-anion difference. Animals fed the positive diet tended to be more susceptible to anorexia.

Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references (leaves 61-66). / vii, 66 leaves, bound ill. 29 cm

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