S. N. McCutcheon

Effect of herbage type and level of intake on the release of chromic oxide from intraruminal controlled release capsules in sheep

Abstract Controlled release capsules (CRC) provide for the continuous uniform release of chromic oxide (Cr2O3) into the rumen and so offer an improved means of estimating feed intake in grazing animals. Two experiments were conducted with sheep to measure the effect of herbage type and level of herbage intake on the pattern of Cr2O3 release from CRC. In Experiment 1, differences in CRC plunger travel within and between rumen-fistulated sheep, fed lucerne chaff indoors over 42 days at an allowance equivalent to 1.1 maintenance (M), were not significant. The relationship between plunger travel and time was almost perfectly linear (P < 0.001), but a slight reduction in the rate of plunger displacement became more pronounced while the animals were at grazing between Day 43 and Day 100. Chromium (Cr) release from Day 3 to Day 42 averaged 62 ± 1 (mean ± SE) mg Cr/day. In Experiment 2, rumen-fistulated and intact wethers, housed indoors, were offered ryegrass, white clover, ryegrass-white clover mixed, or meadow...

Selective enhancement of growth in twin foetuses by shearing ewes in early gestation

Shearing ewes during pregnancy frequently increases the birth weight of lambs. In housed ewes, the birth weight responses are greatest when shearing occurs relatively early in pregnancy. This study examined the effects of the timing and method of shearing on foetal growth, as measured by birth weight, in ewes at pasture. Border Leicester × Romney ewes were allocated at day 50 of pregnancy to: four ‘time of shearing’ treatments — pregnancy day 70 (P70), P100, P130 (no. = 60 for each treatment) and unshorn (no. = 34); two methods of shearing (by standard comb or cover comb); and two levels of pregnancy/rearing rank All ewes had been mated over a 14-day period and grazed pasture together throughout the trial The mid-point of lambing was 17 August. At no time during pregnancy or lactation did ewe live weight differences between the groups exceed 4 kg. Ewes shorn by cover comb were heavier prior to lambing and during lactation than standard comb-shorn ewes. Time of shearing, method of shearing and ewe rearing rank had no effect on ewe annual greasy fleece production. There was a highly significant (P v. single foetuses in utero. This selective increase in birth weights of twins achieved by early pregnancy shearing may have advantages in reducing lamb mortality.

Developmental patterns of plasma insulin-like growth factor-1 concentrations in sheep

A study was undertaken to examine the ontogeny of circulating insulin-like growth factor-1 (IGF-1) concentrations in sheep. The trial was a balanced 2 x 2 factorial design incorporating the effects of sex and rearing rank with a total of 48 animals. Blood sampling was initiated four weeks post-weaning (about 3 months of age) and continued every 2 weeks for 6 months and then every 4 weeks for 7 months. Fecal egg counts and plasma concentrations of non-esterified fatty acids (NEFA) were also determined. IGF-1 concentration was positively related to live weight throughout the trial, even when adjusted to common sex and rearing rank. Sex of lamb had a significant effect on plasma IGF-1 concentrations with concentrations in males being greater than those in females. Puberty in females, as determined by date of first estrus, was associated with an increase in plasma IGF-1 concentrations. Although puberty in males was not measured, a surge in plasma IGF-1 concentrations around the approximate time of puberty in males resulted in a marked divergence between the sexes which remained throughout the study. Rearing rank did not influence plasma IGF-1 concentrations beyond 7 months of age. Plasma IGF-1 concentrations tended to be negatively associated with plasma NEFA concentrations and fecal egg counts but relationships were only occasionally significant. IGF-1 levels were highly repeatable, concentrations at the first sample being significantly correlated with those at all subsequent samples. Implications of these results in relation to potential use of plasma IGF-1 concentration as a genetic marker for productivity are discussed.

Shearing ewes at mid-pregnancy is associated with changes in fetal growth and development

This study investigated the effect of mid-pregnancy shearing (at Day 70 of pregnancy, P70) on herbage intake of grazing single- and twin-bearing ewes, lamb birth weight, and cold resistance of new-born lambs. At pregnancy diagnosis on P50, 30 single-bearing and 30 twin-bearing ewes were allocated either to be shorn at P70 (n = 15 for each pregnancy rank) or to remain unshorn to serve as controls (n = 15 for each pregnancy rank). All ewes were mated over a 3-day period with synchronisation of their oestrus. Herbage intake was measured indirectly from in vitro pasture digestibility and faecal output of grazing ewes, with the use of intra-ruminal chromium slow-release capsules, over six 5-day periods from P64 to P105. The weights of placental and fetal tissues were assessed in a subgroup of 16 ewes at P140 and P141. In the remaining sheep, lamb liveweight at birth and during lactation until weaning at 103 days of age was measured, and cold-resistance of new-born lambs was assessed by measuring summit metabolic rate (SMR) by indirect calorimetry. Ewe liveweight (corrected for fleece weight), condition score, and herbage intake during pregnancy were not affected by shearing treatment. Mid-pregnancy shearing did not affect placental weight, but increased the relative weights (i.e. g/kg liveweight) of fetal thyroid gland and lungs and reduced the relative weight of adrenal glands and heart. The ratio of secondary to primary wool follicles in near-term fetal skin was about 10% higher in offspring of shorn than of unshorn ewes. The metabolic rate of fetal hepatic tissue was increased by mid-pregnancy shearing, particularly in twin fetuses, possibly indicative of an increase in placental transport of nutrients to the fetuses. This conclusion is supported by the greater birth weight (average response 0.5 kg) of lambs born to ewes shorn at mid-pregnancy. Mid-pregnancy shearing also increased the SMR of new-born twin lambs by 16%, but decreased the SMR of singleton lambs by 26%. These results indicate that mid-pregnancy shearing can increase lamb birth weight without increasing ewe herbage intake or placental weight. An increase in the efficiency of nutrient uptake by the placenta is implied, and possible effects on the activity of thermogenic tissues are discussed.

Maternal constraint and the birthweight response to mid-pregnancy shearing

Pregnancy shearing has been shown to increase lamb birthweights. However, results have been variable between studies. It has been suggested that the birthweight response to pregnancy shearing is greatest in conditions in which the unshorn dam gives birth to lambs of low birthweight. This study was designed to examine the birthweight response under 2 differing maternal treatments (one designed to restrict fetal growth and the other designed not to limit fetal growth), with the aim of explaining the variation observed in pregnancy shearing studies. Mixed aged Romney cross ewes were either shorn during mid pregnancy (n = 55) or left unshorn (n = 50). At shearing, ewes were split into either a ‘maintenance’ group (64 kg at shearing and fed to permit total ewe liveweight gain equivalent to expected conceptus growth during mid- to late-pregnancy) (n = 52) or a ‘low’ group (54 kg at shearing and fed to permit total ewe liveweight to increase at half the expected conceptus growth during mid- to late-pregnancy) (n = 53), respectively. Mid-pregnancy shearing was found to increase the birthweights of singletons (5.6 v. 4.9 kg, P < 0.05) but not twins, and of lambs born to maintenance group ewes (by 0.6 kg, P < 0.05), but not low group ewes. Additionally, mid-pregnancy shearing had no effect on the thermoregulatory capacity of twin-born lambs. When the results of this study are considered with those of previous New Zealand pregnancy shearing studies, they suggest that there are 2 criteria (and not one, as previously suggested) that must be met to achieve a response to pregnancy shearing. Firstly, the dam must have the potential to respond [i.e. have been destined to give birth to an otherwise lightweight lamb(s)], and secondly, the ewe must have the means to respond (i.e. an adequate level of maternal reserves and/or level of nutrition to partition towards additional fetal growth).

Responses to divergent selection for plasma concentrations of insulin-like growth factor-1 in mice

A divergent selection experiment with mice, using plasma concentrations of insulin-like growth factor-1 (IGF-1) at 42 days of age as the selection criterion, was undertaken for 7 generations. Lines were not replicated. To obtain sufficient plasma for the IGF-1 assay, blood from four individuals was volumetrically bulked to obtain a litter mean IGF-1 concentration. This necessitated the use of between family selection. Although inbreeding accumulated in a linear fashion in each of the high, control and low lines, the rates were different for each line (3.6, 1.6 and 5.3% per generation for the high, control and low lines, respectively). As a consequence, the effects of selection and inbreeding are confounded in this experiment. Divergence between the high and low lines in plasma concentrations of IGF-1 continued steadily until generation 5. In generations 6 and 7, there was a reduced degree of divergence and this contributed towards the low realized heritability value of 0.15 +/- 0.12. Six-week liveweight showed a steady positive correlated response to selection for or against plasma concentrations of IGF-1 until generation 4 (high-low difference = 1.7 g = 12%). In generation 5, a substantial drop in 6-week liveweight in the low line relative to both the high and control lines occurred (high-low difference, 3.9; g, 25%). This difference was maintained until generation 7.(ABSTRACT TRUNCATED AT 250 WORDS)

Shearing during pregnancy — review of a policy to increase birthweight and survival of lambs in New Zealand pastoral farming systems

Abstract Over the past decade, lambing percentages have risen in conjunction with a rise in the percentage of multiple lambs born. Multiple-born lambs are smaller than their singleton counterparts and are particularly susceptible to starvation-exposure. Any technique that can increase the birthweight or thermoregulatory capability, or both, of otherwise lightweight lambs has the potential to substantially increase survival of multiple-born lambs. In the United Kingdom under housed conditions, shearing during pregnancy has been shown to increase both the birthweight and thermoregulatory capability of newborn lambs. However, shearing during pregnancy under pastoral conditions has failed to consistently affect the newborn lamb’s thermoregulatory capability. In contrast, under New Zealand’s pastoral conditions shearing during pregnancy has been found to increase birthweight, but results have been inconsistent in both magnitude and birth-rank specificity. Increase in feed intake by the dam, types of shearing comb used and changes in gestation length do not explain the variation observed. When studies involving shearing during pregnancy are collated it becomes apparent that there are two criteria that must be met to achieve a birthweight response. Firstly, the dam must have the potential to respond and secondly, the dam must have the means to respond. Any increase in lamb survival through shearing during pregnancy would be predominantly through an increase in birthweight of otherwise lightweight lambs. However, in the few studies conducted to date, an increase in birthweight has not resulted in a statistically significant increase in survival. For an increase in birthweight to have a positive effect on lamb survival, lambs must be otherwise destined to be born within a birthweight range in which survival rate is below optimum (<4.0 kg), and the increase in birthweight observed must move a significant proportion of otherwise lightweight lambs into a higher range of survival rate.

Plasma metabolite and hormone concentrations as predictors of dairy merit in young Friesian bulls: effect of metabolic challenges and fasting

Responses to metabolic challenges were measured in 8-month-old Friesian bull calves with a view to identifying possible predictors of genetic merit for milk fat production. Seven ‘high’ breeding index bulls (mean breeding index for milk fat = 128·9 (s.d. 4·8) percentage units) were compared with six ‘low’ breeding index bulls (mean 107·3 (s.d. 2·4) percentage units). Bulls were from two selection lines and breeding indices calculated as the average of parental breeding index values. Challenges involved intravenous injection of the following (dose rates per kg body weight): adrenalin (1 μg); glucose (0·17 g); glucagon (0·175 μg); insulin (0·01 mg); and arginine (40 mg). Blood samples were withdrawn prior to and after each challenge (two challenges daily). Bulls were then fasted for 3 days before being refed. Relative to the low breeding index bulls, those in the high breeding index group exhibited: (a) greater pancreatic sensitivity to circulating glucose as indicated by increased insulin concentrations following the glucose challenge; (b) more rapid clearance of glucose from plasma following the insulin challenge; (c) reduced sensitivity to the glycogenolytic/gluconeogenic effects of glucagon as indicated by lower blood glucose concentrations following intravenous injection of this hormone; (d) elevated plasma insulin and growth hormone concentrations during the fasting period; (e) elevated plasma concentrations of insulin, glucose and urea during refeeding; (f) no difference in responses to intravenous arginine or adrenalin, or in circulating concentrations of Insulin-like Growth Factor-1 or alkaline phosphatase. Results are consistent with previous observations that metabolic differences between cattle in the Massey University high and low breeding index lines are most evident in the metabolism of glucose and insulin. Metabolic challenges offer a potentially useful means of predicting genetic merit for milk fat production but the conditions under which repeatable differences between the lines can best be demonstrated are yet to be determined.

The effects of nutritionally-induced liveweight differences on follicular development, ovulation rate, oestrous activity and plasma follicle-stimulating hormone levels in the ewe

Abstract Romney ewes of similar mean liveweight were differentially grazed to generate two treatment groups (n = 35) differing in mean liveweight by approximately 15 kg. Oestrous cycles were synchronized by treatment for 14 days with intravaginal sponges, and the oestrous activity and ovulation rate (O.R.) for the cycle immediately following sponge withdrawal recorded. Patterns of preovulatory follicular development, ovarian antral follicle populations and plasma FSH levels were compared between the two treatment groups during the second cycle following sponge withdrawal. Ewes in the high-liveweight (HLW) group had a significantly (P 2 mm in diameter and more follicles in the terminal stages of atresia than those in the LLW group. There was no difference between the two groups in plasma FSH levels during the late luteal and follicular phases. These results suggest that variation in ovulation rate due to nutritionally-induced difference in liveweight is associated with changes in the patterns of ovarian follicular development, changes which appear to be independent of circulating levels of FSH.

Effects of pre‐lamb shearing on feed intake and associated productivity of May‐ and August‐lambing ewes

Abstract The effects of pre‐lamb shearing on feed intake and wool/lamb production of May (autumn)‐ and August (spring)‐lambing ewes were examined. Mixed age Border Leicester x Romney ewes mated to lamb in May or August (60 ewes/ lambing policy) were divided at random into two groups (balanced for pregnancy status and liveweight). One group was shorn on Day 118 of pregnancy (P118) and the second group left unshorn. Measurement of pasture intake was carried out over three periods before lambing (P113–117, P119–130, and P141–144) and three periods after lambing (L (lactation day) 8–11, L21–25, and L29–33) using intraruminal chromic oxide controlled release capsules. Intake of ewes was not affected by shearing treatment during pregnancy or lactation except during P141–144 when organic matter intake was significantly greater for shorn ewes than for unshorn ewes (1739 ±58 versus 1526 ± 59 g/day, P < 0.05). Ewe liveweights and condition scores were similar for both shearing treatments during pregnancy and lactat...