T. W. Knight

Effect of dietary vitamin A on plasma and liver carotenoid concentrations and fat colour in Angus and Angus crossbred cattle

Abstract The effect of dietary vitamin A supplements on plasma carotenoid (PC), liver B‐carotene, and fat carotenoid concentrations, and on fat colour in cattle were determined in three experiments. In Experiment 1, thirteen 2‐year‐old Angus × Friesian steers were grazed on pasture, and 6 of the steers were supplemented daily with 1 × 106 IU vitamin A for 83 days. In Experiment 2, twenty 2‐year‐old Angus crossbred heifers were grazed on pasture with 5 being supplemented daily with 1 × 106 IU and 5 with 2.5 × 106 IU vitamin A for 31 days. Cattle in Experiments 1 and 2 were slaughtered at the end of the experiments, and liver and fat samples were analysed for retinol and carotenoid concentrations respectively in Experiment 1, and liver samples were analysed for both retinol and carotenoid concentrations in Experiment 2. Experiment 3 involved ninety 3‐year‐old Angus steers, 10 of which were slaughtered at the beginning of the experiment, 20 were grazed on pasture, and the remaining 60 steers were fed a diet ...

Factors affecting the variation in fatty acid concentrations in lean beef from grass‐fed cattle in New Zealand and the implications for human health

Abstract Lean beef from grass‐fed cattle was analysed for fatty acid (FA) content to determine the between‐animal variation and the effects of various traits on FA composition, and indices and FA ratios that have human health implications. In Experiment 1, samples were from three muscles from five bulls, five cows, and five heifers. In Experiment 2, samples were from the m. longissimus lumborum of 50 3/4 Jersey 1/4 Limousin and 50 3/4 Limousin 1/4 Jersey cattle, born over 2 years and sired by two bulls. The heifers and steers grazed on similar pastures until slaughter. In both experiments, after adjusting for differences in total FA content of the meat, there were large coefficients of variation (CV) for trans‐vaccenic, cis‐9 trans‐11 conjugated linoleic, and docosahexaenoic acids and low CV for the saturated (SATFA) and monounsaturated FA (MUFA), and intermediate CV for other FA. There were significant effects of muscle and animal types in Experiment 1 and of breed, sire, sex, and year‐born in Experiment 2 on the composition and content of individual and groups of FA, especially the polyunsaturated FA (PUFA). The n‐6:n‐3, PUFA:SATFA, and MUFA: SATFA ratios, and the indices for atherogenicity and thrombogenicity, traits that have human health implications, were affected by factors in both experiments, but absolute differences were small. The conclusions were that the FA composition of lean grass‐fed beef could be changed by traditional means to improve the human health image of beef, but the impact would be small and progress slow. More progress was likely from selecting for beneficial FA than against undesirable SATFA.

Effect of interval from castration of bulls to slaughter on carcass characteristics and meat quality

Abstract A trial was conducted to see whether reducing the interval from castration to slaughter could produce steer‐like carcasses but retain the weight advantage of bulls. Ninety Angus, Friesian × Hereford, and Friesian × Simmental bulls were allocated to nine groups. Four groups were castrated at 8 months of age (steers), and three groups were castrated on January 17 (Day 0) at 17 months of age (castrates). One group of bulls and one group of steers were slaughtered on Day 5, groups of steers and castrates were slaughtered on Days 62, 111, and 166, and the remaining group of bulls was also slaughtered on Day 166. On Day 0, bulls and steers were 455 ± 6 and 426 ± 5 kg liveweight, respectively. Liveweight gain of castrates was lower than that of steers for 106 days following castration and the carcass weight (CW) advantage of bulls over steers at 17 months of age was lost in castrates slaughtered at Day 62. The rate of change in carcass, meat, and fat characteristics varied with the attribute under consi...

Effect of method of castrating bulls on their growth rate and liveweight

Abstract Bulls were castrated surgically or using a Callicrate™ Bander (Bander) to compare the effects on growth rate and liveweight. In Experiment 1, 20 bulls were castrated surgically (SCasts) at 14 months of age and 19 bulls were castrated with the Bander (BCasts). Within 7 days of castration the BCasts had large wounds above the band. Growth rates were lower (P < 0.01) over the first 29 days after castration for BCasts than for SCasts and both groups grew slower (P < 0.05) than steers castrated at weaning. There was no significant difference in liveweight between groups 108 days after castration. In Experiment 2, 10 bulls were castrated surgically at 8–9 months of age and 10 bulls were castrated with the Bander. BCasts grew slower (P < 0.05) over the first 35 days after castration than SCasts, resulting in lower liveweight for BCasts than SCasts (P < 0.05) 35–122 days after castration. No lesions occurred in the BCasts. The banding technique does not prevent the slow growth rates found after surgical castration and banding should only be used on bulls less than 14 months of age.

Foetal mortality at different stages of gestation in alpacas (Lama pacos) and the associated changes in progesterone concentrations

Abstract From spring 1990 to autumn 1993, 44 spring-mated and 82 autumn-mated alpacas at Flock House Agricultural Centre (FH) had their pregnancies monitored by ultrasound every 10–14 days from day 20 to day 120 of gestation. A further 32 autumn-mated alpacas at Tara Hills High Country Research Station (TH) were monitored in 1992. Trans-rectal probes were used in early gestation and trans-abdominal probes in late gestation. As techniques for pregnancy diagnosis in alpacas improved during the experiment, the stage of gestation at which pregnancies were first confirmed became earlier. From spring 1991 onwards most pregnancies were first diagnosed at 20–30 days of gestation. Progesterone concentrations were determined from individual blood samples collected each time alpacas were brought in for pregnancy diagnosis from spring 1991 onwards. Foetal loss from day 30 onwards was 25.7% with the foetal losses after day 120 of gestation being 9.6–16.7% in different mating groups. There were apparent differences in the pattern of foetal loss between autumn- and spring-mated alpacas at FH with foetal losses before day 81 being 17.3% and 2.8% respectively and no significant difference in foetal loss after day 81 of gestation. The younger New Zealand born alpacas had a similar incidence of foetal loss to the older Chilean born alpacas. There was a suggestion at TH that the stress of transport and relocation of a group of alpacas at 212 ± 3 days of gestation precipitated a high incidence of foetal loss. The spring-mated alpacas had a longer gestation length (350.1 ± 2.7 days) than autumn-mated alpacas at FH (340.2 ± 1.9 days).

Effects of dietary carotene content on mean values and rankings of heifers for plasma carotene concentrations

Abstract An experiment was conducted with six Angus (AH) and six Jersey (JH) heifers to determine the effects of dietary carotene on plasma carotene concentrations (PCC) and the consistency of the ranking of heifers on PCC. The heifers were divided into high, medium, and low liveweight groups and each group of four heifers was placed in a separate pen on a feedpad. The heifers were fed pellets comprising 25% lupin and 75% barley grain and containing either 500,250, or 0 mg added carotene/ kg pellets. The pellets were fed at 1.1% of the mean liveweight of each group. Barley straw was available ad libitum. Pellets were given in a sequence as follows: pellets with 500 mg added carotene/kg were given for 27 days followed by those with 250 mg added carotene/kg for 21 days, and 0 added carotene/kg for 70 days. Blood samples were taken every 2–4 days and analysed for PCC. There were no significant effects of breed on PCC except for a more rapid increase in PCC in JH than AH when returned to pasture after being o...

Conservation of conjugated linoleic, trans‐vaccenic and long chain omega‐3 fatty acid content in raw and cooked lamb from two cross‐breeds

Abstract Available literature mainly describes the fatty acid (FA) content of raw meat, with only limited data explaining the effect of different preparation and cooking temperatures on health‐promoting FA such as conjugated linoleic acid (CLA), its metabolic precursor trans‐vaccenic acid (TVA), and long chain omega‐3 FA (LC omega‐3 FA). We collected m. longissimus thoracis (LT) from rib chops of Poll Dorset × East Friesian (EF) and Poll Dorset × Romney (R) lambs raised together. The FA composition of raw LT was compared with LT prepared with bone and all fat trimmed away or bone and fat left intact before cooking under a fan‐grill. The LT from EF lambs had less cooking loss, lower lipid and total fatty acid (TFA) contents, and a lower proportion of saturated fatty acids (SATFA) than the LT from R lambs. Raising cooking temperature from medium to well‐done increased cooking losses and dry matter (DM) yield but did not affect FA content or composition. Compared with raw LT, cooking of the trimmed LT resulted in more TFA and lipids in the DM, and these were greater still in the intact LT. Similar increases occurred in the DM content of most individual and groups of FA, except for CLA and LC omega‐3 FA which increased with cooking of trimmed LT without further significant increase with cooking intact LT. The proportions of SATFA and TVA in the TFA increased after cooking trimmed LT and increased further after cooking intact LT. In contrast, proportion of polyunsaturated fatty acid (PUFA) was reduced at each step, while the proportion of CLA was not affected by cooking. Thus, the FA content of raw lamb underestimates that of cooked meat, especially if the lamb is cooked with bone and fat left intact allowing infiltration of FA from the surrounding intermuscular and subcutaneous fat. This influx of lipids from the surrounding adipose tissue dilutes the proportions of PUFA and LC omega‐3 FA in the TFA.

Effects of suckling regime on lamb growth rates and milk yields of Dorset ewes

Abstract Poll Dorset ewes on a commercial sheepmilking enterprise were used in two experiments to determine the effects of restricted access of lambs to ewes on milk yield and composition, and on lamb growth rates. In Experiment 1, 75 ewes were allocated to four treatments: control (C) ewes whose lambs were artificially reared and the ewes milked twice a day; once-a-day (OAD) ewes whose lambs were artificially reared but the ewes were milked once a day; night-suckling (NS) ewes which had access to one lamb for 16 h following afternoon milking; and day-suckling (DS) ewes which had access to one lamb for 8 h following morning milkings. The NS and DS ewes were milked once a day before the lambs had access to the ewes and after weaning the ewes were milked twice a day. Total milk yields over the 91 days of milking were 141.1 ± 6.4 1 milk for C ewes and 15% (20.5 1) and 17% (24.5 1) lower for NS and DS ewes respectively. OAD ewes produced 48% less milk than C ewes over the lactation which was 15–16 days shorte...

Effects of shearing on milk yields and milk composition in machine-milked Dorset ewes

Abstract Four experiments were conducted to determine the effects of shearing before lambing or during lactation on the yield and composition of milk from machine-milked Dorset ewes. In Experiments 1 and 2, ewes were shorn in early lactation and although no effects on milk yield were recorded, there were significant increases (8–24%) in the concentrations of fat and protein in the milk. Experiment 3 included ewes which were shorn 12–52 days before lambing or 1–23 days after lambing. Shearing before or after lambing increased the concentrations of fat, protein, and total solids in the milk. For the ewes shorn before lambing, the percentage of lactose was lower. In Experiment 4, Dorset ewes were shorn in early lactation (20–28 days after lambing) or late lactation (47–56 days after lambing). Shearing increased the concentrations of fat, protein, and total solids in both groups of ewes but had no effect on milk yield. There were no effects of shearing in early lactation on percentage lactose but the ewes sho...

Effects of milking frequency and machine‐stripping on the yield and composition of milk from Poll Dorset ewes

Abstract Mature Poll Dorset ewes from the Flock House commercial sheep‐milking flock in their 9th week of lactation, were used in two experiments. In Experiment 1, 40 ewes were used to compare the effects of missing an afternoon milking every 7 days with control ewes which were milked twice every day. In Experiment 2, 60 ewes were used in a 2 × 2 factorial comparing once‐a‐day versus twice‐a‐day milking and no machine‐stripping versus machine‐stripping. The results indicated that reducing milking frequency after the 8th week of lactation had no effects on the duration of lactation and only a small effect on total lactation yield. The 7% lower milk yields resulting from missing one afternoon milking every 7 days represented a loss of only 1.6 1 milk/ewe, and the 19.4% reduction in milk yield after the 8th week of lactation from once‐a‐day milking represented a loss of only 7.9 1 milk/ewe. The concentration of protein was higher in the milk from ewes missing a milking in Experiment 1 (6.40 ± 0.08% for ewes ...