D. M. McNeill

Microbial interactions with tannins: nutritional consequences for ruminants

Polyphenolics are widely distributed in the plant kingdom and are often present in the diet of herbivores. The two major groups of plant polyphenolic compounds other than lignin are condensed and hydrolysable tannins. These compounds can have toxic and/or antinutritional effects on the animal. It is well established that tannins complex with dietary proteins can reduce nitrogen supply to the animal, but the ability of gastrointestinal microorganisms to metabolise these compounds and their effects on microbial populations have received little attention. In this paper, we review recent literature on the topic as well as present research from our laboratories on the effect of condensed tannins on rumen microbial ecology and rumen metabolism. Interactions of tannins with dietary components and endogenous protein in the rumen and post-ruminally, and their impact on the nutrition of the animal are considered

The effect of fasting on liveweight and carcass characteristics in lambs.

In two experiments, involving 250 and 300 lambs, respectively, lambs were fasted (with access to water) and slaughtered after 0, 1, 2, 3 and 4 days. The effects of initial fat score, initial liveweight and sex (wethers and ewes) on the patterns of loss in liveweight, hot carcass weight and carcass characters (fat depth at the GR and C sites, kidney fat weight and the weights of chemical carcass components) were examined. In experiment 2 the effects of weaning and transport on fasting losses were also examined. The rate of liveweight loss (expressed as a percentage of initial liveweight) was greater in the initial stages of the fast and was affected by fat score, with a greater loss in lambs with a lower fat score. The pattern of loss in hot carcass weight with fasting was curvilinear and in experiment 2 was affected by both fat score and liveweight, with leaner, heavier lambs having a greater loss. In experiment 2 the decrease in fat depth at the GR site interacted with fat score, with a greater loss in lambs with a lower fat score. Transport per se had no effect on hot carcass weight or carcass characteristics.

The partition of nutrients in ewes maintained in a moderate compared with a lean body condition in late pregnancy

The efiect of ewe fatness on fetal weight at term was tested without the confounding efiects of placental weight and feed intake. We hypothesised that fetal weights should be similar in fat or lean ewes with placentas of a similar size, and tested the hypothesis by manipulating nutrition so that, at mating, Merino ewes carrying a single fetus were in a medium (score 2¢9, liveweight 46¢ 6k g) or lean (score 2¢ 0, liveweight 40¢ 6 kg) condition. They were maintained at this fatness difierence until slaughter at Day 146 of pregnancy when fetal, placental, and maternal tissues were weighed and analysed for composition. Subgroups (n = 8 per fatness group) slaughtered at Day 110, a stage when most placental hypertrophy is complete but the majority of fetal hypertrophy is yet to occur, conflrmed that the treatments difiered in ewe fatness (3¢82 v .9 ¢19 kg empty-body fat, s:e:m: =0 ¢960; P 0 ¢05). By Day 146, fatness difierences (4¢77 v .9 ¢56 kg empty-body fat, s:e:m: =0 ¢960, P 0 ¢05) were maintained, and both groups produced fetuses of similar size (4408 v. 4382 g, s:e:m: = 204¢ 6, P> 0 ¢05). However, the fetuses in the lean ewes had 20% less fat/kg fat-free body weight (24 v. 30 g/kg, s.e.m. = 1¢ 3, P< 0 ¢01). Fetal weight was correlated with placental weight (r =0 ¢70 ;P < 0 ¢01) but not with ewe fatness. Fetal fatness, however, was correlated with ewe fatness (r =0 ¢69 ;P< 0 ¢01). Ewe fatness per se did not in∞uence fetal size but did in∞uence the deposition of fat in the fetus, possibly via a greater ability of fatter ewes to partition more glucose toward their fetus.

Influencing the future: interactions of skeleton, energy, protein and calcium during late gestation and early lactation

Marked improvements in milk production, health and reproduction have resulted from manipulations of the pre-calving diet. An understanding of the underlying physiological changes resulting from manipulation of late gestational diets is needed in order to refine and enhance these responses. The physiology of late gestation and early lactation of the dairy cow is examined in the context of exploring the hypothesis that changes in physiology occur not only through homeostatic, but also homeorhetic change. Studies in mice and man have identified a pivotal role for skeleton, particularly through production of active forms of osteocalcin, in integrating energy metabolism. Skeleton appears to particularly influence lipid metabolism and vice versa. Further insights into the factors influencing skeletal function and calcium (Ca) metabolism are emerging, including the potential for negative dietary cation anion difference (DCAD) diets to upregulate the responses of the skeleton in metabolism through increased bone mobilisation and in enhancing responses to parathyroid hormone. The rumen appears to be an important site of absorption of Ca, but physiological mechanisms influencing this uptake are not clear. We provide quantitative evidence of the magnitude of responses that reflect relationships linking Ca metabolism, skeleton and production, using meta-analytic methods. Negative DCAD diets increase milk production in multiparous cattle, but not in heifers. Further, examination of concentrations of metabolites related to energy metabolism obtained from cattle exposed to a negative DCAD diet over calving identified a dominant role for Ca concentrations, which were associated with blood-free fatty acids (NEFA), blood 3-hydroxybutyrate, glucose and cholesterol. These relationships were homeostatic, occurring on the same day, but also homeorhetic with concentrations of Ca and NEFA being significantly associated over 21 days. The findings in cattle are consistent with those in the murine models. However, Ca and the skeleton are not the only significant factors in the transition period influencing future performance as hormonal treatments, metabolic demands and sex of the conceptus, and inflammation and the factors controlling this play a role in future performance. Homeorhetic, longer-term, adaptive responses are critical to achieving orchestrated longer-term adaptive responses to calving and lactation. We consider that the teleological question ‘why would a bone-specific hormone (osteocalcin) regulate energy metabolism?’ is answered by the specific needs for integrated metabolism to address the extreme metabolic demands of lactation in many species.

Insulin sensitivity and fetal growth in ewes maintained in a moderate body condition compared with a lean body condition in late pregnancy

The possibility that an increase in maternal fatness might further enhance pregnancy-induced insulin insensitivity was investigated in ewes pregnant with one fetus. After selection of fat and lean ewes, they were fed to maintain maternal energy balance throughout pregnancy. A difierence in insulin sensitivity of ewes in either a medium condition (score 2¢9, 0¢ 32§0¢ 031 kg fat/kg fat-free empty body (FFBW), n = 7) or lean body condition (score 2¢ 0, 0¢ 16§0¢ 028 kg fat/kg FFBW, n = 8) at Day 136 of pregnancy was inferred by comparing their insulin response to an injection of glucose (350 mg/kg liveweight). The ewes were slaughtered at Day 146 of pregnancy to allow fetal weight, fetal fatness, and maternal fatness to be related to the capacity of the ewe to release insulin. The fatter ewes released more insulin in response to the injection of glucose (2¢54 log area units under the insulin response curve v .2 ¢22 for the lean ewes, pooled s.e. = 0¢ 092, P < 0¢ 05), yet cleared the glucose from their blood streams at the same rate as the leaner ewes. Because the fat ewes required more insulin to remove a similar amount of exogenous glucose at a similar rate to the lean ewes, we suggest that the fat ewes were less sensitive to insulin. Further, the fetuses of the fatter ewes, while not difierent in total weight, had higher levels of body fat than those of the leaner ewes (29¢ 4 v. 23¢ 8 g/kg FFBW, pooled s.e. = 1¢32, P < 0¢ 05). Fetal fatness was also positively correlated to the magnitude of insulin release by the ewe (r =0 ¢61, P < 0¢ 05). Since glucose is the major precursor of fetal fat, these data support our contention that a reduction in maternal insulin sensitivity, brought on by an increase in maternal fatness, could partition more glucose to the fetus. If fat reserves aid lamb survival, lambs from fat ewes rather than lean ewes may have a better chance of survival, particularly in cold conditions.

Carryover effects of potassium supplementation on calcium homeostasis in dairy cows at parturition

The purpose of this study was to test whether supplementation with K improves bone mineral density (BMD) in older cows so that by parturition their bone is better able to mobilize Ca. Twenty-four Holstein Friesian cows (6 mo pregnant, lactating, and in their third or later lactation) were allocated to 2 equal groups and individually fed twice daily a total diet comprising low K oaten hay plus a pelleted concentrate fortified with or without K(2)CO(3) to achieve 3.12% K/kg of DM in the total diet of the K-supplemented (KS) cows compared with 1.50% K/kg of DM for the control cows. The cows were fed their respective diets from the beginning of their sixth month of pregnancy until 2 wk before the expected date of parturition. The strategy was to use K to stimulate a mild increase in extracellular pH to potentially improve BMD well before parturition, when high K contents in the diet are considered safe, but cease supplementing in the few weeks prepartum, when high intakes of K are known to be problematic. The expectation was that the effect of the denser bone would carry through to benefit the cows plasma Ca, P, and Mg status at parturition. Prior to the period of K supplementation, the cows were part of a commercial pasture-based herd, to which they were returned at the end of the supplementation period and treated as 1 group from at least 11 d prepartum until the end of the study at d 42 of the next lactation. Supplementation with K successfully induced a sustained increase of urinary pH throughout late lactation and into the dry period, as expected. The KS cows consistently averaged a urine pH 0.25+/-0.10 U higher than the controls. However, there was no significant effect of K supplementation on BMD, bone mineral concentrations, plasma osteocalcin, urinary deoxypyridinoline:creatinine plasma Ca, or plasma P concentrations during or immediately after the cessation of supplementation, nor where there any carryover effects during parturition or by d 42 of lactation. Instead, there was an unexpected decrease in the concentration of Mg in plasma of the KS cows compared with the control cows that extended from 0.5 to 2.5 d postpartum. The timing of the decline in plasma Mg was paralleled by declines in plasma concentrations of 1,25 dihydroxy-vitamin D(3) and urinary excretion of Ca and Mg, whereas urinary excretion of P increased; all changes were consistent with a hypomagnesemia that could increase the risk of hypocalcemia. These data suggest that, in addition to the well-documented negative effects of K when fed immediately at parturition, the effects of high dietary K diets can carry over for at least 11 d to trigger a mild hypomagnesemia at parturition. Because K supplementation did not improve BMD prepartum, it was not possible to conclude for or against an ability of denser bone to reduce the risk of hypocalcemia in older cows at parturition.

Blood lactose v. milk lactose as a monitor of lactogenesis and colostrum production in Merino ewes

The pattern of onset of lactation and colostrum production was compared in 42 single- and twin-bearing Merino ewes of 2 genotypes, Australian Merino Society (AMS) or Meridale (AMS with an infusion of British Breeds). The onset of lactation was indicated by measuring changes in the concentration of lactose in udder secretions (milk lactose) and in blood samples (blood lactose) collected daily for at least 4 days prior to, and at 1, 3, 6, 12, and 24 h after, parturition. Blood lactose was a novel alternative to milk lactose, as blood was easier to collect than udder secretions. Colostrum production was measured by milking the ewes at 1, 3, and 6 h after parturition. Twin-bearing ewes initiated lactation later than single-bearing ewes, but both groups produced similar volumes of colostrum to I h after birth (475 v. 371 mL, P > 0.05). The rate of secretion of colostrum was similar for twin-and single-bearers in the interval 1-6 h after birth (82 v. 79 mL/h, P > 0.05). Meridale Merinos secreted colostrum at a faster rate than the AMS Merinos at 1-6 h post-partum (94 v. 67 mL/h, P < 0.05), but had similar accumulations of colostrum to the AMS Merinos before birth. Five percent of ewes had no colostrum available Ih after birth. The concentration of blood lactose reflected changes in milk lactose prior to, but not after, the first few hours post-partum.-Blood lactose concentration measured prior to birth was related to the volume of colostrum that had accumulated in the udder up to Ih after birth (r = 0.60, P < 0.001), but milk lactose measured at the same time was not related to the accumulation of colostrum. Blood lactose measured before birth can be used to estimate whether treatment groups of ewes differ in the volume of colostrum available for the lamb at birth. This may permit us to study the relationship between lamb survival and colostrum production in the field without disturbing the ewe-lamb bond by milking the ewe.

Maternal fatness influences fetal size in ewes underfed in late pregnancy

The effect of ewe fatness on fetal weight at term in ewes underfed in late pregnancy was tested by minimising the confounding effect of differences between fatness groups in placental weight. Twin-bearing Merino ewes in a fat (n = 9, condition score 3.8 units) or moderate (n = 9, condition score 2.9) body condition were underfed to 0.6 of their requirements for energy maintenance from Day 108 to 144 of pregnancy. The fatness groups were developed over an 80-day period prior to mating by splitting a flock into 2 groups, each of similar mean liveweight and body condition score, and then enhancing the nutrient intake of one whilst restricting that of the other to maintenance levels until mating. After mating, both groups were fed similarly until Day 108 of pregnancy in an attempt to allow the development of placentas of a similar size in each. Maternal fat and protein mobilised between Day 108 and 144 of pregnancy were calculated on a per animal basis as the difference between maternal fat and protein weights at Day 108, estimated by the tritiated water dilution technique, and at Day 144, estimated by chemical analysis of fat and protein tissue following slaughter. At slaughter, the fat ewes had placentas of a size similar to those of the leaner ewes (588 v. 507 g, pooled s.e. = 50.7, P > 0.10) but produced a total weight of fetus that was 14% heavier (6646 v. 5826 g, pooled s.e. = 257.6, P 0.10) over late pregnancy. We conclude that additional maternal fat reserves can limit the extent to which fetal growth is restricted in ewes undernourished during late pregnancy.

Partition of nutrients in moderately fat ewes compared with lean ewes given ad libitum access to feed in late pregnancy

The effect of a difference in voluntary feed intake on fetal weight was tested in lean v. moderately fat ewes (0.15 v. 0.32 kg/kg fat-free empty body weight), by giving them ad libitum access to feed from Day 110 to 146 of pregnancy when both had placentas of a similar size (at Day 146: 437 v. 461 g, s.e.m. = 49.5, P > 0.05). Although the lean ewes ate 29% more than the fatter ewes above their estimated requirements (1258+/-106.9 v. 978+/-105.8 g/ewe.day, P=0.08) fetal weights were not affected (4744 v. 4590 g, s.e.m. = 282.1, P > 0.05). Instead, the lean ewes partitioned more of their intake into body fat than the fatter ewes (0.13 v. 0.01 kg/kg fat-free empty body weight, P < 0.05). The results support the concept that the placenta places an upper limit to the uptake of nutrients by the fetus.

Metabolic and production responses to calcidiol treatment in mid-lactation dairy cows

The study of vitamin D in cattle has often focussed on its role in calcium and mineral metabolism. However, there is evidence of a wider role for vitamin D in bone and energy metabolism. Two studies were conducted to explore relationships between calcidiol supplementation, blood minerals and metabolites in mid-lactation dairy cows. In Experiment 1, a dose-response study was conducted in which 25 mid-lactation cows were fed one of five supplementary calcidiol doses (0, 0.5, 1, 2 or 4 mg calcidiol/day) for 30 days, with blood samples taken every 10 days. Increasing calcidiol dose increased plasma calcidiol (P = 0.001), 24,25-(OH)2-D3 (P = 0.001) and serum phosphate (P = 0.003) in a curvilinear manner, increased and then decreased plasma 25-OH-D2 (P = 0.004) and linearly increased 3-epi 25-OH-D3 (P = 0.001) and milk calcidiol concentrations (P = 0.001). Calcidiol supplementation did not affect milk yield or composition, bodyweight or condition score. In Experiment 2, relationships between blood calcidiol and mineral and metabolite concentrations over time were explored using time-series analysis. Ten mid-lactation cows were fed either 0 or 0.5 mg calcidiol/day for 27 days, with blood samples taken every 3 days. Feeding calcidiol increased plasma calcidiol (P = 0.001), 24,25-OH-D3 (P = 0.038), and insulin (P = 0.046), but decreased 25-OH-D2 (P = 0.008) concentrations. Positive associations were identified between blood calcidiol and concentrations of other metabolites, including cholecalciferol, calcium, osteocalcin, glucose, insulin, non-esterified fatty acids, β-hydroxybutyrate, cholesterol, magnesium, phosphorus and total protein at varying lags (±0, 3 or 6 days), while negative relationships were identified between calcidiol and 24,25-(OH)2-D3, and phosphorus 3 days later. Importantly, strong positive associations between calcidiol and indicators of energy metabolism were identified. Overall, these experiments provide support for a positive effect of calcidiol treatment on dairy cow metabolism.