The nutrition of grazing ewes during pregnancy and lactation: relationships between herbage, supplement and milk intakes, and ewe and lamb liveweight and body composition

This paper reports results from a study of ewes in pregnancy and lactation, during which times they grazed at a high versus medium stocking rate and either received or did not receive a pelleted supplement. We measured ewe liveweight, condition score and body composition; intakes by ewes of pasture and supplementary feed; milk production by ewes, and; birthweight, milk intake, liveweight gain and body composition of single and twin lambs. Ewes grazing at the medium stocking rate consumed more pasture in late pregnancy and the intake of supplement significantly reduced pasture intake. Nevertheless, total intakes of organic matter or digestible organic matter were unaffected by supplementation and were significantly higher at the medium stocking rate. Effects of stocking rate on intake persisted into early and mid-lactation, but supplement intake did not affect pasture intake in lactation. Pasture intakes in pregnancy were not markedly different between twin-bearing and single-bearing ewes, nor were pasture intakes in lactation affected by the number of lambs suckled. Ewes suckling twins produced much more milk. There were significant effects of birth type, ewe stocking rate and supplementation on lamb milk intake and liveweight gain. The data were reanalysed by regression, to explore the effects of actual herbage masses and ewe intakes, and the possible effects of non-treatment terms such as ewe age, condition score and dentition score at allocation. These analyses confirmed the above effects of treatment, but also demonstrated that ewes in better condition at the start of the experiment ate less pasture in both pregnancy and lactation, and produced significantly less milk. Ewe organic matter intakes in pregnancy were not related to dentition score at allocation, but in early and mid-lactation were reduced by ~170 g organic matter/day and 280–380 g organic matter/day, respectively, per unit increase in dentition score. There was no significant effect of ewe dentition score on lamb milk intake, but there was a significant penalty of ~19 g lamb liveweight gain/unit increase in ewe dentition score at allocation. Future studies of this kind thus need to include estimates of the condition score and dentition score of ewes when they commence the experiment.

Milk intake and growth rate of Awassi lambs sucking ewes grazing on natural pasture in the semi-arid Negev

We determined milk intake and growth rate of fat-tailed Awassi ram lambs from birth to 30 days of age when sucking ewes that were grazing natural green pasture in the semi-arid Negev. The conversion of milk and energy intake to body mass and body solids gain in the lambs were calculated. Annual rainfall and, as a consequence, pasture availability were below average during the study. Body mass at birth was 4·22 (s.d. 0·71) kg and at 30 days was 12·10 (s.d.1·22) kg for an average daily gain of 256 (s.d.33) g/day. Of the 256 g/day, 100 (s.d.12·3) g/day were body solids, and for every unit body mass increase, proportionately 0·391 was body solids. Milk and energy intakes averaged 1·34 (s.d.0·23) l/day and 5·66 (s.d.0·97) MJ/day, respectively. The volume of milk intake per kg increase in body mass and body solids were 5·2 l and 13·4 l, respectively, whereas, the energy intake per kg increase in body mass and body solids were 22·1 MJ and 56·6 MJ, respectively. Of the total metabolizable milk energy intake, proportionately 0·46 was converted to body energy of the lamb. Although dry matter intake of the ewes was insufficient to prevent body mass loss, they produced sufficient milk to support a relatively high lamb growth rate, presumably by mobilizing fat reserves in the tail.

Estimation of colostrum intake in the neonatal pig

Three trials were performed in order to establish a method of estimation of colostrum intake based on weight gain in newborn pigs. The first trial involved 33 piglets, bottle-fed with sow colostrum and weighed regularly for 25 h. A regression equation relating colostrum intake (CI in g) to birth weight (BWB in kg), weight at CI estimation (BW in kg), age at first suck (tFS in min) and duration of colostrum intake (t in min and with 17 h < t < 25 h) was established with a root mean-square error equal to 33 g. This equation was evaluated with a second data set using 15 further bottle-fed piglets (trial 2). Measured and predicted values were very close (R2 = 0.90). The third trial compared colostrum intake estimated either with the previous equation or with the deuterium oxide dilution method in catheterized sow-reared or bottle-fed piglets (no. = 12 per group). The equation underestimated colostrum intake of those piglets, probably due to prior surgery. However, the feeding method (bottle-feeding v. sow-rearing) had no effect on the relationship between weight gain and colostrum intake. Therefore, the equation established in bottle-fed piglets may be applied to sow-reared piglets.

Stomach temperature records reveal nursing behaviour and transition to solid food consumption in an unweaned mammal, the harbour seal pup (Phoca vitulina)

Knowledge of milk transfer from mother to offspring and early solid food ingestions in mammals allows for a greater understanding of the factors affecting transition to nutritional independence and pre-weaning growth and survival. Yet studies monitoring suckling behaviour have often relied on visual observations, which might not accurately represent milk intake. We assessed the use of stomach temperature telemetry to monitor suckling and foraging behaviour in free-ranging harbour seal (Phoca vitulina) pups during lactation. Stomach temperature declines were analysed using principal component and cluster analyses, as well as trials using simulated stomachs resulting in a precise classification of stomach temperature drops into milk, seawater and solid food ingestions. Seawater and solid food ingestions represented on average 15.3±1.6% [0–40.0%] and 0.7±0.2% [0–13.0%], respectively, of individual ingestions. Overall, 63.7% of milk ingestions occurred while the pups were in the water, of which 13.9% were preceded by seawater ingestion. The average time between subsequent ingestions was significantly less for seawater than for milk ingestions. These results suggest that seawater ingestion might represent collateral ingestion during aquatic suckling attempts. Alternatively, as solid food ingestions (n = 19) were observed among 7 pups, seawater ingestion could result from missed prey capture attempts. This study shows that some harbour seals start ingesting prey while still being nursed, indicating that weaning occurs more gradually than previously thought in this species. Stomach temperature telemetry represents a promising method to study suckling behaviour in wild mammals and transition to nutritional independence in various endotherm species.

A note on milk intake of piglets measured by tritium dilution

The milk intake of two litters of suckling piglets was measured by the turnover of tritium-labelled body water. The estimated intakes of a litter of seven piglets agree with the current knowledge of milk yield from sows, which generally rises to a maximum at the 3rd week and then declines. With a litter of four, intake rose continuously from the 1st to the 6th week. Since piglets are often weaned at 3 weeks of age, this method has few disadvantages n i practical use. During the estimation of water turnover the total body water of individual piglets can also be obtained so that information on body composition (solids, protein, fat and ash) can be derived. The efficiency of conversion of milk by piglets can thus be calculated.

Limits to sustained energy intake VII. Milk energy output in laboratory mice at thermoneutrality

The limits to sustained energy intake at peak lactation could be imposed peripherally, by the capacity of the mammary glands, or centrally, by the capacity of the animal to dissipate body heat generated as a by-product of processing food and producing milk. To distinguish between the two hypotheses,we examined milk energy output at peak lactation in MF1 laboratory mice exposed to 30°C (N=12), 21°C (N=10; published data)and 8°C (N=10; published data). The peripheral limitation hypothesis predicts that milk energy output will remain constant at different temperatures, while the heat dissipation limit hypothesis predicts a decline in milk energy output as temperature increases. Since estimates of milk energy output in small mammals can vary depending on the calculation method used, we evaluated the milk energy output of mice (N=24) using four different methods: (1) as the difference between metabolizable energy intake and daily energy expenditure of the female, (2) from female water turnover, (3) from pup water turnover and (4) from the energy budget of the litter. We assessed these four methods by comparing their accuracy, precision and sensitivity to changes in parameters involved in the calculations. Methods 1, 3 and 4 produced similar estimates of milk energy output, while those derived from female water turnover were significantly lower and more variable. On average, mice at 30°C exported significantly less energy as milk (87.7 kJ day–1) than mice at 21°C (166.7 kJ day–1) and 8°C (288.0 kJ day–1). This reduction in milk energy output at 30°C was caused by a significant decline in both milk flow (20.0 g day–1, 12.9 g day–1 and 8.5 g day–1 at 8°C, 21°C and 30°C, respectively) and gross energy content of milk (14.6 kJ g–1, 13.1 kJ g–1 and 10.5 kJ g–1 at 8°C, 21°C and 30°C, respectively). Milk produced at 30°C contained significantly less total solids (34.4%) than milk at 21°C (40.9%) and 8°C (41.5%) and significantly less fat(20.0%) than milk at 21°C (26.4%) and 8°C (30.3%). The reduced milk energy output in mice exposed to 30°C, paralleled by their reduced food intake and low reproductive output, argues against the peripheral limitation hypothesis and provides strong support for the heat dissipation limit hypothesis.

Is suckling behaviour a useful predictor of milk intake? A review

In studies on mammalian parental investment, time spent suckling is often used as a predictor of the milk transferred from mother to infant. It is assumed that the rate of milk transfer is positively correlated with the time spent suckling. However, this assumption has not been tested and empirical studies show conflicting results. Nevertheless, in species in which suckling can readily be observed, time spent suckling is still used to measure milk transfer, although an increasing number of workers recognize that the measure is potentially inaccurate. A meta-analysis on studies that have correlated measures of time spent suckling with milk intake estimates based on weight gain revealed a weak positive relationship and significant heterogeneity between studies. Isotope-labelling techniques for the measurement of milk transfer independent of behaviour have been in use since the 1970s, particularly in studies of species in which suckling is difficult to observe. Only one study has attempted to correlate behavioural measures with independent isotope measures, and it found no relationship between the two measures. I suggest that researchers have avoided such a test as it is unlikely that a strong relationship will be found between milk transfer and suckling behaviour, and I discuss the various factors that confound the relationship and contribute to high heterogeneity between studies. Consequently, the assumption that milk transfer can be measured by time spent suckling has inadequate empirical foundation, and needs to be tested using isotope-labelling methods. Copyright 1998 The Association for the Study of Animal Behaviour

Daily milk intake and body water turnover in suckling mink (Mustela vison) kits

Daily (24 h) milk intake and body water turnover were measured in eight litters of suckling mink (Mustela vison) kits (6-9 kits litter-1) during weeks 1-4 post partum using the tritiated water (3HHO) dilution technique. The biological half-life of body water turnover in the mink kits increased linearly from 0.9 days in week 1 (3-5 days post partum) to 1.9 days in week 4 (22-24 days post partum). The daily milk intake varied markedly among the mink kits within a litter and increased significantly with increasing body mass from (mean +/- SEM) 10.9 +/- 0.4 g per kit during week 1 to 27.7 +/- 1.0 g per kit during week 4. Throughout the study, male kits were approximately 10% heavier and had a significantly higher milk intake than female kits. The results were corrected for water recycling between the dam and her kits, ranging from approximately 4 to 15% of the daily milk water intake, and the calculated daily milk yield of the 2 year old lactating mink dams increased from 87 +/- 7 g day-1 in week 1 to 190 +/- 15 g day-1 in week 4 post partum. The average body growth rate of the mink kits ranged from 2.9 g kit-1 per day in week 1 to 5.4 g kit-1 per day in week 4, and the calculated mean intake of mink milk per unit of body weight gain was remarkably stable at 1.0 (g g-1) during weeks 1-3 post partum, but increased to 5.6 (g g-1) in week 4 post partum. The amount of metabolizable energy supplied to the kits by the daily milk yield of the dam increased from approximately 450 to approximately 990 kJ day-1, which corresponded well with the calculated daily energy requirements of the kits. The tritiated water dilution technique was found feasible and reliable for repeated measurements of milk intake in suckling mink kits up to 4 weeks of age.

Milk consumption and growth in a marsupial arboreal folivore, the common ringtail possum, Pseudocheirus peregrinus

This study examines the milk consumption and growth energetics of the smallest arboreal folivore in Australia, Pseudocheirus peregrinus. Mass increase was sigmoidal, and young ceased sucking milk between 27 and 30 wk (mean = 29.3 +/- 1 wk). This length of lactation was 129% of that predicted allometrically from data for other marsupials. The mean Gompertz constant (0.01) calculated for seven young suggests that P. peregrinus has a slow rate of growth compared with other marsupial species. Milk intake was measured with isotopic turnover techniques. The estimated total milk energy yield (11.9 MJ kg-1) for a ringtail possum suckling two young was similar to that of the only other marsupial herbivore for which data are available (Macropus eugenii). However, peak milk energy output (154.4 kJ kg-0.75 d-1) was lower than that in other herbivores. The body mass accrued from milk consumption by young ringtail possums at various stages of lactation was similar to that of other marsupials, suggesting that the slow rate of growth in this species is a result of a limited rate of supply of milk energy from the mother and not an inefficient conversion of milk energy in the young.

Lactation, hibernation, and mass dynamics of American black bears and grizzly bears

Milk composition and intake, cub growth, and mass loss of hibernating lactating and nonlactating American black bears (Ursus americanus) and grizzly bears (Ursus arctos horribilis) were investigated. Except for ash content, milk composition was similar between species. Lipid content varied only slightly throughout lactation, whereas carbohydrate content increased from 1 to 3% during hibernation before decreasing to less than 0.5% at the end of lactation. Protein and dry matter content increased from 6.6 ± 0.4 and 29.8 ± 3.9% during hibernation to 13.7 ± 1.1 and 34.4 ± 3.7% post hibernation, respectively. The ash content of black bear milk increased from 1% during hibernation to 2% after den emergence, but the ash content of grizzly bear milk (1.3 ± 0.1%) did not fluctuate. Mean milk intake and growth during hibernation were 185 ± 89 and 49 ± 9 g/day for black bear cubs and 353 ± 54 and 98 ± 22 g/day for grizzly bear cubs, respectively, which accounted for about 9% of the estimated yearly milk consumption by the cubs. Milk intake peaked during the summer at levels approximately 4 times higher than those occurring in the winter den. The mass lost by older, hibernating, nonlactating bears was proportional to their metabolic body mass and was almost exclusively lipid. The rate of mass loss by denning, lactating females relative to nonlactating bears was 45% higher for black bears and 95% higher for grizzly bears. The less costly black bear cub may be at an important competitive advantage when both species occupy nutritionally limited habitat.

Nutrition and growth of suckling black bears (Ursus americanus) during their mothers' winter fast

In black bears the last 6-8 weeks of gestation and the first 10-12 weeks of lactation occur in winter while the mother is in a dormant state, and reportedly does not eat, drink, urinate or defaecate. Measurements were made of the body composition and organ weights of cubs, of the composition of milk, and of milk intake (by dilution of 2H2O), in the first 3 months after birth. Additional milk samples were collected until 10 months postpartum. Bear cubs were small at birth, only 3.7 g/kg maternal weight, and chemically immature, as indicated by the high concentration of water (840 g/kg) in their bodies. Organ weights at birth were similar to those of puppies. In the first month after birth cubs gained 22 g/d or 0.23 g/g milk consumed; the milk was high in fat (220 g/kg) and low in water (670 g/kg). About 30% of the ingested energy and 51% of the ingested N were retained in the body. Over the entire 12-week period bear cubs required about 11 kg milk, containing (kg) water 7, fat 2.5, protein 0.8 and total sugar 0.25, to achieve a 2.5 kg weight gain. The birth of immature young and the production of high-fat, low-carbohydrate milk seem to be maternal adaptations to limit the utilization of glucogenic substrates during a long fast. Isotope recycling indicates that mothers may also recover most of the water (and perhaps much of the N) exported in milk by ingesting the excreta of the cubs. Lactation represents another aspect of the profound metabolic economy of the fasting bear in its winter den.

Milk and water intakes of foals sucking grazing mares

Intakes of milk and milk nutrients were determined for 8 foals at 11-18 days of age and for 10 foals at 30-44 days and 60-74 days of age while sucking grazing mares. Water intakes (sources other than milk) of the foals were determined at 30-44 days and 60-74 days of age. Five of the 10 mares were fed a protein supplement (24% crude protein) in addition to grazing during the stud season. The protein supplement did not influence foal intakes of milk and milk nutrients, milk composition, weight gains of the mares or the growth rate of the foals. Foal milk intakes increased (P less than 0.05) from 16.9 kg/day at 11-18 days to 18.1 kg/day at 60-74 days of age. The water intakes of the foals increased (P less than 0.01) from 3.9 kg/day at 30-44 days to 5.5 kg/day at 60-74 days of age. Total fluid intakes per kg foal liveweight were 246, 202 and 172 g at 11-18, 30-44 and 60-74 days of age, respectively. For each kg of weight gain, foals consumed 12.8, 15.7 and 16.4 kg milk at 11-18, 30-44 and 60-74 days of age. Stage of lactation had a significant effect on the total solids, lactose and protein content of milk. The fat and gross energy content of milk remained constant.

Measurement of milk intake: tracer-to-infant deuterium dilution method

The tracer-to-infant deuterium dilution method for the measurement of milk intake was evaluated in twenty breast-fed and twenty formula-fed infants. The isotope method was compared with conventional direct-weighing techniques. Human milk intake was assessed by 5 d test-weighing. Intakes of formula, supplemental foods, and water were determined by pre- and post-weighing of feeding bottles. An oral dose of 200 mg 2H2O/kg body-weight was given to each infant, and urine was sampled daily for 14 d. 2H enrichment of the urine was measured by gas-isotope-ratio mass spectrometry. Milk intakes estimated from the deuterium dilution method were consistently higher than those from direct-weighing; the mean difference between methods was 106 (SD 47) g/d or 14% for the breast-fed group and 70 (SD 155) g/d or 8% for the formula-fed group. Estimates of intake for some infants varied substantially between the two methods of measurement. When the estimated values of human milk intake were corrected for environmental water influx and insensible water loss during breast-feeding, the relative bias decreased to 5%. Correction of the estimated values of formula intake for environmental water influx decreased the relative bias to 1-2%. The acceptability of the deuterium dilution method to determine milk intake depends on the goals and the tolerance for error in group and individual intake estimates of a given study.

Estimation of the intake of milk by lambs, from the turnover of deuterium- or tritium-labelled water

1. The total water turnovers of grazing ewes and their lambs were estimated on days 9, 23, 44, 69 and 86 of lactation from the dilution of tritiated water injected into the dam and deuterium oxide injected into the offspring. The contribution of milk to the total water turnover of the lambs was estimated at the same times from the accumulation of tritium in their body water. 2. Mean total water turnover in the ewes was 6.5 titres/d over the entire period. In lambs, total turnover rose from 1459 ml/d at 9 d to 2791 ml/d at 86 d, and was closely related to live weight (r2 0.760, P less than 0.001). The corrections to total water turnover, which were required because of the increasing body water pool size of the lambs during each measurement period, fell from + 10.6% at 9 d to + 3.7% at 86 d. All corrections were significant (P less than 0.001). 3. The intake of water as milk fell throughout the study, from 1501 ml/d at 9 d to 471 ml/d at 86 d. Pool-size corrections were significant (P less than 0.001). Milk intakes calculated from these results were 1816, 1054, 862, 742 and 588 ml/d at 9, 23, 44, 69 and 86 d of lactation. The rapid decline in milk intake reflected undernutrition of the ewes in early lactation. 4. The level of live-weight gain in early lactation was closely related to, and at a level expected from, the estimated milk intakes. From comparisons of estimated milk intakes with published estimates, it is concluded that the combined use of deuterium oxide and tritiated water results in accurate estimates of milk intake by the lamb throughout the ewe's lactation.

Analytical procedures for estimating milk intake and yield in steady-state and nonsteady-state systems

A tracer method for determining milk intake, introduced earlier, was based on the transfer of tritiated water from a lactating female to a nuring offspring via milk. The analysis of the tracer data assumed a steady state system, i.e., the total body water of the offspring was assumed to be constant over the measurement period. This paper discusses the potential errors in the milk intake estimates in applications where steady-state does not exist. Three analytical procedures are considered and include the application of 1) steady state equations for a nonsteady-state system, 2) analytical solutions to nonsteady-state equations, and 3) a computer modeling program, SAAM-27. The application of steady-state equations is the simplest procedure and may yield acceptable estimates if the growth rate of the nuring offspring is low. The analytical solution procedure yields acceptable estimates at high growth rates of the nursing offspring but becomes unacceptable at low growth rates. The SAAM program requires sophisticated computer hardware and programming; however, the procedure yields the best estimates of milk intake in applications ranging from steady-state to high growth rates.

The intake of milk by suckled, newborn lambs and the effects of twinning and cold exposure

Clun Forest ewes with single and twin lambs were exposed to neutral (20 degrees) or cold (-1 degree) environmental temperatures, beginning soon after parturition, for 4 d. The intakes of milk, lactose and glycerides by the lambs were calculated from measurements of the rate of displacement of tritiated water (injected into the lambs) by non-radioactive water in milk from the ewes, and measurements of the concentration of lactose and glyceride glycerol in small samples of milk. The yield of milk from ewes bearing twin lambs was greater than the yield from single-bearing ewes in the neutral environment but, in both environments, twin lambs had lower intakes of milk and milk lactose and glycerides, and gained body-weight more slowly, than single lambs. Milk from twin-bearing ewes had a lower lactose concentration than milk from single-bearing ewes. Cold exposure reduced the intake of milk and milk lactose, and reduced the rate of weight gain, of single and twin lambs. Glyceride intake was not different in the two environments. There appears to be a conflict between reduced supply of milk by the ewe and increased demand for milk by the lamb in cold temperatures. Such a conflict is sharpened when twin lambs are born.