Utilization of milk energy by suckling mink kits

A total of 36 mink dams and their litters of 3, 6 or 9 kits were used for determination of milk intake of the suckling young by means of deuterium dilution technique, and chemical composition of milk and of kit bodies. Measurements were performed during lactation weeks 1-4, each week with 3 dams with each litter size. Milk intake was determined over a 48 h measurement period, and by the end of this milk samples were collected and 2 kits (litters of 6 and 9) or 1 kit per litter (litters of 3) were killed for body chemical composition. Based on the results, different models were applied for calculation of the energetic efficiency of milk. Dam milk yield increased steadily from week 1 until week 3 but only slightly from week 3 to 4. The increase declined with increasing litter size, and for dams suckling 9 kits the increment from week 3 to week 4 was only 2 g. The dry matter content of milk increased significantly as lactation progressed, being reflected in crude protein increasing from 6.9% in lactation week 1 to 8.1% in week 4. Milk fat increased concomitantly from 5.6% to 8.0%. In kit bodies, crude protein content increased from 9.4% in week 1 to about 12% in weeks 3 and 4. Body fat content increased from week 1 (4.1%) to week 3 (8.4%) and then declined in week 4 (7.1%). Animals suckled in litters of 3 kits had the highest milk intake and live weight and kits suckled in litters of 9 had the lowest milk intake, live weight and daily gain. In terms of milk intake per g gain kits in litters of 6 were the most efficient, with 4.1 g milk per g body gain. The metabolizable energy requirement for maintenance (MEm) was estimated to 448 kJ/kg(0.75 and the efficiency of utilization of ME for body gain (kg) to 0.67, the estimates being higher (MEm) or in good agreement with previous findings (kg) in suckling mink kits.     

Energy intake and milk production in mink (MUSTELA vison)‐effect of litter size

Energy intake and milk production were measured in 12 mink dams raising litters of 3, 6 and 9 kits one to four weeks post partum by means of balance experiments and measurements of milk intake of the kits by the water isotope dilution technique. The dams were fed ad libitum on a conventional wet mink diet (DM: 323 g/kg; CP: 173 g/kg; ME: 4.4 MJ/kg). Milk samples collected from dams with corresponding litter sizes and lactation weeks, and body composition of kits nursed by these dams, were analysed for content of DM, ash, N and fat. The ME and drinking water consumption were higher in dams nursing 9 kits than in dams nursing 3 kits. The N and water balances as well as the live weight of dams were not affected by litter size. Daily milk production was higher in dams nursing 9 kits than in dams nursing 3 kits. The DM, N and fat content of the milk increased during lactation, but were not affected by litter size. Individual kit live weight was higher in litters of 3 than in litters of 6 and 9 kits four weeks post partum. The DM and fat content of the kits were lowest in kits from litters of 9 kits, whereas these kits had the highest protein content. Daily ME for maintenance of kits and the efficiency of utilisation of ME in milk for body gain were estimated to 356 kJ/kg^0.75, k_p ≈0.53 and k_f ≈0.71, respectively. In conclusion, daily milk production increased with increasing litter size, but not in proportion to the number of kits, indicating that milk production limits the growth rate of the young. In the fourth week of lactation, milk production was not different between dams nursing 6 or 9 kits, indicating a maximum capacity.     

Utilization of milk amino acids for body gain in suckling mink (Mustela vison) kits

The efficiency of utilization of milk amino acids for body gain in suckling mink kits from small (n = 3), medium (n = 6) and large litters (n = 9) was investigated by using 36 mink dams and their litters for measurements during lactation weeks 1 through 4. Measurements on each dam and litter were performed once, hence three dams per litter size each week (n = 9). Individual milk intake of kits was determined, milk samples were collected and kits were killed for determination of amino acid composition. The most abundant amino acids in milk were glutamate, leucine and aspartate making up about 40% of total amino acids. Branched chained amino acids made up slightly more than 20% and sulphur containing amino acids less than 5% of total milk amino acids. In kit bodies the sum of glutamate, aspartate and leucine made up about 32% of amino acids, branched chain amino acids about 16% and sulphur containing amino acids about 4%. The amino acid composition of both milk and bodies changed as lactation progressed with decreasing proportions of essential amino acids. The ratio between body and milk amino acids was constantly over 1 only for lysine, suggesting that it was the most limiting amino acid in mink milk. Milk amino acids were efficiently utilized during week 1, ranging from 74.7% (lysine) to 42.1% (leucine), with an average for essential amino acids of 58.4%. Tendencies for improved utilization of lysine (74.7-78.2%), phenylalanine (61.0-70.0%), histidine (62.4-68.8%), arginine (61.3-70.4%) and all essential amino acids (58.4-60.2%) from week 1 to week 2 were recorded. During weeks 3 and 4, the efficiency declined, and for all essential amino acids the average utilization was 38.1% during week 4.     

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 ∼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 ∼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 4.0 (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 ≈450 to ≈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.     

Dam characteristics associated with pre-weaning diarrhea in mink (<Emphasis Type="Italic">Neovison vison</Emphasis>)

Background

Pre-weaning diarrhea (PWD) in mink, also known as “sticky kits”, is a frequently occurring syndrome in suckling mink kits on commercial mink farms. Outbreaks of PWD result in weakened kits, increased mortality and reduced growth and welfare as well as considerable economic losses for the farmers. The syndrome is regarded as multifactorial with a complex etiology, and studies have focused on associations with environment, management and dam characteristics. The present study was conducted from May to June 2015 and included 70 dams with mink litters with and without PWD. The aims were to examine associations between PWD and mastitis (bacterial infection and histological signs of inflammation or other lesions in the mammary gland), and to examine associations between PWD and other dam-related characteristics (age, litter size, body mass index, and weight and number of active mammary glands of the dam).

Results

Using multivariable mixed logistic regression analyses with farm id as a random intercept, we found that the odds for PWD in the litter were significantly higher in 1 year old dams versus?>?1 year old (OR?=?13.3, CI 2.0–90.2, P?=?0.01), higher if litter size observed after birth was?>?5 kits versus?≤?5 kits (OR?=?16.5, CI 2.2–123.7, P?=?0.01), higher if the number of active mammary glands per kit was?≤?1.5 versus?>?1.5 glands per kit (OR?=?6.5, CI 1.2–36.0), P?=?0.03), and higher in farms with high prevalence of PWD versus low prevalence (OR?=?16.8, CI 2.9–97.6, P?=?0.002). There were no significant associations between PWD and bacterial infection, histological signs of inflammation or other lesions of the mammary gland, body mass index or weight of mammary gland per kit.

Conclusion

Pre-weaning diarrhea had a statistically significant association with age of the dam, litter size and the number of active mammary glands per kit. However, PWD was not associated with mastitis, body mass index and weight of mammary gland tissue per kit.

     

High-protein diet during gestation and lactation affects mammary gland mRNA abundance, milk composition and pre-weaning litter growth in mice

We evaluated the effect of a high-protein diet (HP) on pregnancy, lactational and rearing success in mice. At the time of mating, females were randomly assigned to isoenergetic diets with HP (40% w/w) or control protein levels (C; 20%). After parturition, half of the dams were fed the other diet throughout lactation resulting in four dietary groups: CC (C diet during gestation and lactation), CHP (C diet during gestation and HP diet during lactation), HPC (HP diet during gestation and C diet during lactation) and HPHP (HP diet during gestation and lactation). Maternal and offspring body mass was monitored. Measurements of maternal mammary gland (MG), kidney and abdominal fat pad masses, MG histology and MG mRNA abundance, as well as milk composition were taken at selected time points. HP diet decreased abdominal fat and increased kidney mass of lactating dams. Litter mass at birth was lower in HP than in C dams (14.8 v. 16.8 g). Dams fed an HP diet during lactation showed 5% less food intake (10.4 v. 10.9 g/day) and lower body and MG mass. On day 14 of lactation, the proportion of MG parenchyma was lower in dams fed an HP diet during gestation as compared to dams fed a C diet (64.8% v. 75.8%). Abundance of MG α-lactalbumin, β-casein, whey acidic protein, xanthine oxidoreductase mRNA at mid-lactation was decreased in all groups receiving an HP diet either during gestation and/or lactation. Milk lactose content was lower in dams fed an HP diet during lactation compared to dams fed a C diet (1.6% v. 2.0%). On days 14, 18 and 21 of lactation total litter mass was lower in litters of dams fed an HP diet during lactation, and the pups' relative kidney mass was greater than in litters suckled by dams receiving a C diet. These findings indicate that excess protein intake in reproducing mice has adverse effects on offspring early in their postnatal growth as a consequence of impaired lactational function.     

Activated mammary number and litter size in the mink.

The dependence of activated mammary number on litter size was studied in standard type farmed mink in an attempt to clarify its effects on early kit mortality. The results showed highly positive correlations between litter size and the number of activated teats at 2 days, 4 weeks and 8 weeks of age. Total kit mortality was rather low and independent of litter size. The body weights of the mothers were independent of either litter size or age during the lactation period. The body weights of male kits were of the same order of magnitude in spite of litter size or age until weaning. In female kits, the body weights in the largest litters were lowest at weaning.     

Effects of intermittent suckling on body composition of Iberian piglets weaned at 35 days of age

Piglet body composition at weaning could be a determinant for pig’s viability and may be influenced by factors such as the nutritional management followed during suckling. An experiment was conducted to study whether intermittent suckling (IS) affects body composition at weaning and nutrient and energy retention during a 34-day lactation period in Iberian piglets. Litters were subjected to conventional suckling (CS) or IS (n=10 litters of six piglets per treatment) in two trials. All piglets had ad libitum access to creep feed from day 15 onwards. In IS, piglets were progressively separated from the sow for 6, 8 and 10 h daily during the last week of lactation, whereas in CS piglets had continuous access to their dams. Creep feed intake in litters and BW development of individual piglets were measured throughout the 34-day lactation. Within each litter, both at birth and at weaning (day 35), one piglet was used to assess nutrient retention and body composition by the comparative slaughter approach. During days 29 to 35 of the experiment, daily creep feed intake was greater in IS piglets (IS 124, CS 67 g/piglet, P=0.040), and average daily gain differed significantly between groups (IS 190, CS 150 g/day, P=0.010). BW at weaning was higher in the IS than in the CS piglets (IS 8.19, CS 7.48 kg, P=0.011). Empty-body fat and energy content at weaning were higher in the IS compared with CS litters, as well as fat content in the carcass (P=0.04). The IS treatment did not affect empty-body protein deposition, but significantly increased daily retention of fat, energy, ash and calcium, compared with CS litters (P<0.05). Thus, IS in Iberian piglets seems to enhance feed intake, growth rate and retention of some body components, which may contribute to a higher body fat content at weaning and facilitate the weaning process.     

Lactation in mice fed endophyte-infected tall fescue seed

This study was conducted to assess the effects of endophyte-infected Acremonium coenophialum tall fescue (KY-31) seed (80% infected) on lactation in CD-1 dams and suckling performance of pups as measured by pup survival and growth rates. Twenty-four pairs of mature CD-1 mice were randomly allocated to four dietary treatments: 1) 100% mouse chow ad libitum; 2) 40% endophyte-infected tall fescue seed and 60% mouse chow (w/w); 3) reduced intake (100% chow), adjusted daily to the intake level of Treatment 2; and 4) 60% infected tall fescue seed and 40% chow. The mice were preconditioned on their respective diets for 100 d prior to 96 h of cohabitation between pairs of males and females. At parturition the litters were removed, and each dam was given a litter of six pups of equal weight, size and sex ratio to suckle for 15 days. All pups given to all the dams were born to other mice that were not part of the study and had not been exposed to endophyte-containing diets. Dams and litter weights were measured daily for 15 consecutive days. The combined body weight measurements of litters from dams fed the tall fescue containing diets (Treatments 2 and 4) were significantly lower (2.07 +/- 0.41 g/d) than that of litters from dams fed the chow containing diets (Treatments 1 and 3) during the suckling trial (P<0.05). Similarly, nine of ten (90%) dams fed the chow containing diets maintained five or more pups (5.5 +/- 0.2) throughout the study as compared to five of nine (55.6%) dams fed the tall fescue containing diets that maintained less than five pups (4.5 +/- 0.2).     

Early kit mortality and growth in farmed mink are affected by litter size rather than nest climate

We investigated the effects of nest box climate on early mink kit mortality and growth. We hypothesised that litters in warm nest boxes experience less hypothermia-induced mortality and higher growth rates during the 1st week of life. This study included data from 749, 1-year-old breeding dams with access to nesting materials. Kits were weighed on days 1 and 7, dead kits were collected daily from birth until day 7 after birth, and nest climate was measured continuously from days 1 to 6. We tested the influences of the following daily temperature (T) and humidity (H) parameters on the number of live-born kit deaths and kit growth: T_mean, T_min, T_max, T_var (fluctuation) and H_mean. The nest microclimate experienced by the kits was buffered against the ambient climate, with higher temperatures and reduced climate fluctuation. Most (77.0%) live-born kit deaths in the 1st week occurred on days 0 and 1. Seven of 15 climate parameters on days 1 to 3 had significant effects on live-born kit mortality. However, conflicting effects among days, marginal effects and late effects indicated that climate was not the primary cause of kit mortality. Five of 30 climate parameters had significant effects on kit growth. Few and conflicting effects indicated that the climate effect on growth was negligible. One exception was that large nest temperature fluctuations on day 1 were associated with reduced deaths of live-born kit (P<0.001) and increased kit growth (P=0.003). Litter size affected kit vitality; larger total litter size at birth was associated with greater risks of kit death (P<0.001) and reduced growth (P<0.001). The number of living kits in litters had the opposite effect, as kits in large liveborn litters had a reduced risk of death (P<0.001) and those with large mean litter size on days 1 to 7 had increased growth (P=0.026). Nest box temperature had little effect on early kit survival and growth, which could be due to dams’ additional maternal behaviour. Therefore, we cannot confirm that temperature is the primary reason for kit mortality, under the conditions of plenty straw access for maternal nest building. Instead, prenatal and/or parturient litter size is the primary factor influencing early kit vitality. The results indicate that the focus should be on litter size and dam welfare around the times of gestation and birth to increase early kit survival in farmed mink.     

Effect of food restriction on reproduction and lactation in house mice mated post partum

Primiparous, post-partum mated BALB/c bom inbred mice were allowed to raise litters of 6 young until Day 22 of lactation: 11 of 25 females were restricted to 60% of food consumption of ad-libitum fed dams after stud male removal at Day 2 of lactation. Since weight gain of restricted females during lactation was not inhibited and infanticidal behaviour was not enhanced, food deprivation can be considered to have been relatively mild. However, none of the food-restricted dams gave birth to a second litter whereas 12 of the 14 ad-libitum fed mice littered. This pregnancy failure is suggested to be due to implantation failure or abortion shortly after implantation, which is attributed to maternal manipulation rather than to immediate consequences of energetic demands of lactated young. The dynamics of the weight changes of dams and young suggest that milk production in suckling house mice drops most markedly between Days 17 and 18 of lactation, irrespective of whether the dams are non-pregnant, pregnant, or food-restricted.     

Milk yield in lines of mice selected for growth or maternal ability.

Two experiments were conducted to measure milk yield as a correlated response to selection for increased 12-day litter weight (maternal lines) for 13 generations and increased and decreased body weight gain from 21 to 42 days of age (postweaning gain lines) for 12 to 14 generations. Milk yield was measured from day 6 to day 21 of lactation by separating litters from their dams for 6 h, then weighing litters before and after a 1.5 h suckling period. Average total milk production was 30.3 +/- 0.9 g and 28.6 +/- 1.1 g in maternal and control lines, respectively. This difference was not significant (P greater than 0.05). Differences among gain lines were significant (P less than 0.01) in the second experiment with average production of 44.1 +/- 1.4 g for increased gain lines, 22.5 +/- 0.9 g for the decreased gain line and 31.2 +/- 1.0 g for the control. These results indicated that response to selection for increased 12-day litter weight was not associated with increases in milk yield, but sizable changes inmilk yield accompanied bi-directional selection for early postweaning gain.     

Mink with Divergent Activity Levels have Divergent Reproductive Strategies

Stable individual differences in activity levels within populations have been linked to differences in reproductive rate or parental care in several species, including American mink (Neovison vison). Fur‐farmed mink are good models for studying such effects because they yield large sample sizes and readily allow investigations into maternal behaviour, reproductive success, offspring performance and the relationships between these factors. On farms, very inactive individuals generally have smaller litters, and this held true in our study populations. We tested two competing hypotheses to explain this: (1) inactive individuals are failing to cope with a challenging environment and experiencing chronic stress and/or depression‐like ‘apathy’; this predicts female‐skewed litters, poorer maternal care, higher infant mortality and poorer infant growth and (2) inactive individuals do not have reduced fitness but instead employ an alternative adaptive reproductive strategy, trading off offspring quantity for quality; this predicts enhanced maternal care, reduced infant mortality and enhanced infant growth. Inactive females’ kits, especially their sons, grew faster than active females’, even after statistically controlling for litter size; and by 21 d, inactive and active dams’ litters no longer differed in total biomass, despite the former’s smaller litter sizes. In kit retrieval tests, inactive females were faster than active dams to reach their sons (as well as more likely to contact their sons than their daughters: a bias towards male kits not evident in the active dams). Furthermore, kit growth rates and dam latencies to touch them co‐varied, suggesting the existence of consistent differences in maternal style across inactive and active dams. Hypothesis 2 was thus supported: inactive females favour offspring quality over quantity, investing more resources in fewer kits, particularly males. This potentially boosts their sons’ adult fitness. More broadly for laboratory‐based studies, possible ‘captivity effects’ on the fitness correlates of activity and other personality traits are discussed.     

Changes in digestive enzyme activity, intestine morphology, mucin characteristics and tocopherol status in mink kits (Mustela neovision) during the weaning period

Weaning of livestock mammals is often associated with digestive problems related to profound changes in the physiology of the gastrointestinal tract. This study was undertaken to study the developmental changes in the gastrointestinal tract of mink kits during the period of 34 to 59 days of age. Twenty-four mink kits from eight litters were included in the experiment. The dams and their litters were kept under standard farm conditions. The dams and the kits were fed a diet consisting of 48.1% protein, 40.7% fat and 11.1% carbohydrate of metabolizable energy. The mink kits were weaned at 42 days of age. At 34, 47 and 59 days of age, one male mink kit from each litter was euthanized. The activity of amylase, trypsin, chymotrypsin and lipase in the pancreatic tissue increased during the experimental period, whereas the activity of carboxyl ester hydrolase remained constant. The vitamin E concentration in plasma was stable from 34 to 59 days of age, whereas the concentration decreased in the liver. The stereochemical composition of α-tocopherol showed a steep decrease in the concentration of the biologically most active natural isomer in both plasma and liver through the whole weaning period, whereas the biologically less active 2S isomers showed a clear increase. The concentration of bile salts did not change during the experimental period. The villous height increased in the proximal part of the small intestine and decreased in the distal part, whereas the crypt depth was doubled in both the proximal and distal part of the small intestine. The mucin-staining area on the villi was markedly reduced during the experimental period but no change in the mucin-staining area in the crypts was observed.     

Interaction of late pregnancy and lactation in rats.

The effect of pregnancy on lactation was studied during the third week of lactational pregnancy in postpartum pregnant rats with a delay in implantation of only 1 day (1d-LP rats). In an experimental design in which the suckling litter was prevented from consuming solid food, lactational performance was estimated by weighing the ten-pup suckling litters on days 16-21 of lactation or by measuring maternal weight loss after a nursing spell on day 21. In 1d-LP rats, food consumption as well as lactational performance was lower than it was in nonpregnant lactating rats (L rats) and pregnant-lactating rats with a normal long delay of implantation of at least 6 days (LP rats). The time spent by the pups sucking at the nipples was not different among the three groups, but the number of milk ejections was diminished in 1d-LP dams. Restriction of daily food supply during days 16 to 21 of lactation diminished lactational performance more strongly in 1d-LP rats than it did in L rats; 1d-LP rats conserved protein stores and mobilized fewer minerals than did L rats. The weight and composition of the litter in vitro were not affected by the food restriction. In pregnant-lactating rats (LP and 1d-LP rats), the number of early resorptions was increased in comparison with pregnant rats, showing that lactation can affect the earlier stages of pregnancy. It was concluded that late pregnancy does not affect nursing behaviour, but suppresses lactation by restricting maternal food intake and mobilization of maternal stores. Measurements in serum indicate a causative role for oestradiol, but not for leptin.     

Metabolic and growth response of mink (Neovison vison) kits until 10 weeks of age when exposed to different dietary protein provision

Growth performance and metabolism were investigated in mink kits (n = 210) exposed to the same dietary treatment as their dams (n = 30), i.e. high (HP; 61% of metabolisable energy, ME), medium (MP; 48% of ME) or low (LP; 30% of ME) protein supply, from birth until 10 weeks of age. The kits were weighed weekly, and were measured by means of balance experiment and indirect calorimetry, in weeks eight and nine post-partum (p.p.). At weaning (seven weeks p.p.) and 10 weeks p.p. one kit per litter was killed and blood, liver and kidneys were collected. Plasma amino acid profiles, and hepatic abundance of mRNA for phosphoenolpyruvate carboxykinase (PEPCK), fructose 1,6-biphosphatase, pyruvate kinase and glucose-6-phosphatase (G-6-Pase) by q-PCR, were determined. There were no differences in live weights among kits the first four weeks of life when kits solely consumed milk, but male LP kits were the heaviest. After transition to solid feed MP kits weighed most at nine weeks of age (p < 0.05). At eight weeks of age, the kits fed the LP diet retained less (p < 0.05) N than HP and MP kits. Heat production did not differ among kits, although protein oxidation was higher (p < 0.001) in HP kits than in LP kits. Kits fed the LP diet had lower (p < 0.05) plasma concentrations of lysine, methionine and leucine than MP kits. Dietary treatment was not reflected in the relative abundance of any of the studied mRNAs, but kits had significantly lower abundance of all studied mRNA than their dams, ranging from 83% less PEPCK abundance to 40% less for G-6-Pase. The kidney mass was smallest (p < 0.01) in kits fed the LP diet, and liver masses were largest (p < 0.001) in HP kits. The results indicate that the LP diet did not meet the protein requirements for mink kits in the transition period from milk to solid feed. The capacity to regulate the rate of gluconeogenesis was even more limited in young mink kits than in adult dams. However, young mink kits can regulate protein oxidation in response to dietary protein supply, probably by adapting the size of the liver and kidneys to the level of protein supply.     

Effect of chronic treatments with ghrelin on milk secretion in lactating rats

Ghrelin, a novel acylated peptide and endogenous ligand for growth hormone (GH) secretagogue receptor, was originally isolated from rat and human stomachs. In addition to its GH-releasing activity, ghrelin plays an important role in many physiological functions, including food intake, gastric acid secretion, neonatal development, and so on. In this study, the effect of daily treatment with ghrelin on milk production was investigated in lactating rats and the development of the pups was monitored. Daily subcutaneous injection of ghrelin into nursing dams for 8 days from parturition caused a significant increase in milk yield and litter weight gain. When litters nursed by ghrelin-treated and saline-treated dams were interchanged on day 4 of lactation, the growth curves were reversed. Daily injections of ghrelin also increased plasma GH levels. Northern blot analysis revealed that daily injection of ghrelin significantly increased mammary casein mRNA expression. In addition, RT-PCR analysis showed that a ghrelin receptor was present in the mammary glands of lactating rats. These results suggest that ghrelin may play an important role in milk production in lactating dams.     

The effect of heat incubators on chilled mink kits

Hypothermia is considered a major risk factor increasing kit mortality in farmed mink. We studied the effects of reheating chilled mink kits. From each of 27 litters, three 1-day-old kits were exposed to one of three treatments: (i) chilling and reheating in a farm incubator (INCU), (ii) chilling and reheating in home nest (HOME), and (iii) control, remained in nest (NEST). During cold exposure (8 °C) mink kits were active in average 67% of the time before they turned inactive; the latency until inactivity averaged 12.3 (0.8) min. We suggest that kit behaviour during early cooling may function to increase chances of eliciting maternal care, and we found that duration of kit activity increased with body weight in 1-day-old kits (P < 0.001). In addition, the most active kits had a shorter latency of coming inactive (P = 0.002), suggesting that the behaviour is energy costly. The kit mortality was low (5 out of 81), making statistical analysis of mortality infeasible. We found no treatment effects on weight gain over 7 days. We did not find any additional effect of the traditional incubator used in reheating chilled 1-day-old mink kits, as the dam in the home nest appeared as efficient to reheat a small chilled kit.     

Effect of a negative energy balance induced by feed restriction in lactating sows on hepatic lipid metabolism,milk production and development of litters

In rodents, forced activation of hepatic peroxisome proliferator-activated receptor α (PPARα) by administration of exogenous PPARα activators during lactation leads to a reduction of milk triacylglycerol (TAG) production. Herein, we investigated whether a negative energy balance (NEB) induced by feed restriction (about 18% lower feed and energy intake) during lactation by increasing the release of fatty acids, which act as PPARα agonists, causes a disruption of hepatic lipid metabolism and thereby impairs milk TAG production in sows. Nutrient and energy content of the milk on day 20 of lactation and gains of litters during the first 14 d and the whole 21 d suckling period did not differ between Control and feed-restricted sows. The mRNA concentrations of several sterol regulatory element-binding protein target genes involved in lipid synthesis in the liver and the plasma concentration of TAG were reduced in the feed-restricted sows, whereas the mRNA concentrations of PPARα target genes involved in fatty acid oxidation in liver and skeletal muscle were not different between groups. In conclusion, it was shown that an NEB during lactation does not adversely affect milk composition and gains of litters, despite inhibiting hepatic expression of genes involved in lipid synthesis and reducing plasma TAG concentration. The finding that PPARα target genes involved in fatty acid utilisation in liver and muscle of sows are not induced by the NEB during lactation may explain that fatty acid availability in the mammary gland is sufficient to maintain milk TAG production and to allow normal litter gain.     

Sows with high milk production had both a high feed intake and high body mobilization

Selection for increased litter size have generated hyper-prolific sows that nurses large litters, however limited knowledge is available regarding the connection between milk production, feed intake and body mobilization of these modern sows. The aim of the current study was to determine what characterized sows with high milk production and nursing large litters, differences between sows of different parities and effects of lactational performance on next reproductive cycle. In total 565 sows (parity 1 to 4) were studied from 7 days before farrowing until weaning. On day 2 postpartum litters were standardized to 14 piglets. Weight and back fat thickness of sows were measured at day 7 prepartum, day 2 postpartum and at weaning. Litters were weighed at day 2 and at weaning. Pearson correlation coefficients between variables were calculated and regression models were developed. The average daily feed intake (ADFI) of the sows was 6.1±1.1 kg/day, average daily gain (ADG) of the litter was 2.92±0.53 kg/day and sows weaned 13.0±1.1 piglets. First parity sows generally had a lower ADFI and milk production and a decrease in total born piglets in next litter compared with parity 2 to 4 sows, which could be explained by a relatively higher proportion of their body reserves being mobilized compared with multiparous sows. The ADG of the litter was positively related by ADFI of the sows, litter size and BW loss and increasing the ADFI with 1 kg/day throughout lactation likely increased the ADG of the litter with 220 to 440 g/day in parity 1 to 4, respectively. Increasing the ADFI by 1 kg/day reduced the BW loss with 6.6 to 13.9 kg of parity 1 to 4 sows, respectively, during lactation, whereas increasing the average milk yield with 1 kg/day raised the BW loss with 4.3 to 21.0 kg of the four parities during lactation. The number of total born piglets in the next litter was positively related to the number of piglets born in the previous litter. In conclusion, both a high feed intake and a high mobilization of body reserves was a prerequisite for a high milk production. The sows might be very close to the physical limit of what they can ingest and future research should therefore, focus on optimizing the dietary energy and nutrient concentrations of diets for lactating hyper-prolific sows and herein distinguish between primiparous and multiparous sows.