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Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance
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Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance W.H.E.J. van Wettere a,∗ , S.J. Pain b , P.E. Hughes c a b c
School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy SA 5371, Australia Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North 4442, New Zealand Pig and Poultry Production Institute, SA 5371, Australia
a r t i c l e
i n f o
Article history: Received 26 April 2016 Received in revised form 5 September 2016 Accepted 9 September 2016 Available online xxx Keywords: Lactation Piglet Reproduction Ractopamine Sow
a b s t r a c t Excessive mobilization of body reserves during lactation delays the return to reproductive function in weaned primiparous sows. This study tested the hypothesis that supplementing the lactation diets of first-parity sows with ractopamine hydrochloride would reduce maternal weight loss and improve subsequent reproductive performance. Gestating gilts were allocated to one of two treatment groups (n = 30 sows/treatment), with one group fed a standard lactation diet (2.5 g/Mcal LYS: DE) throughout lactation (CTRL), whereas the treatment group received the standard lactation diet supplemented with 10 mg/kg ractopamine hydrochloride (RAC) from d 1 to 13 of lactation and 20 mg/kg RAC from d 14 of lactation until artificial insemination (AI). Weaning occurred on d 21 of lactation, with AI occurring at the first post-weaning estrus. Compared to CTRL, RAC supplementation decreased (P < 0.05) liveweight loss between d 13 and 20 of lactation (4.3 ± 0.90 versus 1.3 ± 0.96 kg), and tended to increase (P = 0.06) the number of second litter piglets born alive (9.5 ± 0.52 versus 8.1 ± 0.74). Treatment (RAC versus CTRL) reduced milk protein levels on d 13 and 20 of lactation (P < 0.05), and piglet weight gain between d 13 and 20 of lactation (260 ± 0.01 versus 310 ± 0.01 g/day, P < 0.01). In conclusion, it is evident that dietary RAC altered milk composition and stimulated conservation of maternal body reserves during the third week of lactation, resulting in a beneficial effect on subsequent reproductive performance. © 2016 Elsevier B.V. All rights reserved.
1. Introduction High incidences of premature culling of sows reduce the productivity of the breeding herd and overall herd feedconversion efficiency. Reproductive failure, particularly after the first lactation, is the primary reason for culling primiparous sows (Hughes and Varley, 2003). The high
∗ Corresponding author. E-mail address: [email protected] (W.H.E.J. van Wettere).
milk yield of modern sow genotypes, combined with the innate reduction in appetite of primiparous sows, results in insufficient feed consumption during the first lactation to meet requirements for maintenance, milk production and body growth (Clowes et al., 1998). The resultant nutritional deficit stimulates the catabolism of body reserves (Clowes et al., 2005), with high levels of tissue mobilization, from both fat reserves and skeletal protein, a primary cause of the delay, or failure, of primiparous sows to return to reproductive function post-weaning (Einarsson and Rojkittikhun, 1993; Clowes et al., 2003). High levels of protein mobilization during the first lactation suppress activity
http://dx.doi.org/10.1016/j.anireprosci.2016.09.009 0378-4320/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: van Wettere, W.H.E.J., et al., Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance. Anim. Reprod. Sci. (2016), http://dx.doi.org/10.1016/j.anireprosci.2016.09.009
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Table 1 Composition of the standard lactation sow diet. Ingredient
Nutrient composition, calculated
Item
%
Nutrient
Quantity
Barley Wheat Peas Soyabean meal Meat meal Fish meal Tallow Choline chloride Lysine − HCL d, l-Methionine l-Threonine Mineral mix Salt Limestone
57.0 14.25 10.0 6.0 5.0 2.5 3.75 0.045 0.14 0.025 0.01 0.25 0.3 0.75
Dry matter, % MCal/kg DE Crude Protein, % Fat, % Fibre, % Calcium, % Lysine, % Available lysine, % Methionine, % Threonine, % Tryptophan, % Salt, % Sodium, % Choline, ppm
89.9 3.34 18.7 6.21 4.2 1.0 1.0 0.84 0.31 0.62 0.19 0.54 0.18 1318.3
of the hypothalamic-pituitary-ovarian axis (Quesnel et al., 2005), extends the weaning to estrus interval (Jones and Stahly, 1999) and reduces post-weaning ovulation rate (Mejia-Guadarrama et al., 2002). It is, therefore, reasonable to suggest that if protein mobilization during the first lactation can be reduced, or prevented, then subsequent reproductive performance will be improved and level of culling among primiparous sows will be reduced. The addition of ractopamine hydrochloride, a widely used adrenergic agonist, to the diet of finishing swine increases net protein accretion, most likely due to a combination of increased protein synthesis and decreased protein degradation (Bell et al., 1998; Ross et al., 2011). The current study tested the hypothesis that dietary inclusion of ractopamine during the first lactation would reduce mobilization of maternal body reserves and lactating sow weight loss, resulting in improvements in subsequent reproductive performance. 2. Materials and methods 2.1. Animals This experiment was conducted at the University of Adelaide’s Piggery, Roseworthy, South Australia, with approval from the animal ethics committee of The University of Adelaide. The experiment was conducted in 4 replicates, with the first 2 replicates conducted in spring and 2 more conducted in autumn/winter. 2.2. Experimental treatments, housing and feeding Gestating Large White gilts (n = 60) were weighed and P2 back fat was ultrasonically measured on day 110 of gestation. From day 110 of gestation until weaning, sows were housed in temperature controlled farrowing accommodation, with a temperature range of 17 to 24◦C. Gilts were blocked by body weight (BW) and P2 backfat and allocated to 1 of 2 lactation treatment groups (n = 30 sows/treatment): first-parity sows that were fed a standard lactation diet (CTRL; 3.34 Mcal/kg DE, 18.7%CP, 6.2% crude fat, 4.2% crude fibre, and 2.5 g/Mcal LYS:DE; Table 1) throughout lactation and during the period from wean-
ing to artificial insemination (AI). The other first-parity sows received the same standard lactation diet supplemented with 10 mg/kg ractopamine hydrochloride (RAC; Elanco Animal Health, Macquarie Park, Australia) from days 1–13 of lactation and 20 mg/kg RAC day 14 of lactation until AI. Treatments began 24 h postpartum (designated as d0). During lactation, the amount of feed offered each day was stepped-up gradually, reaching a maximum offered of 6 kg/day the 4th d of lactation (3 meals/d), and daily feed disappearance was recorded for each sow. Pigs were weaned at 21 d of age, and all sows received 3 kg/day of their treatment diets between weaning and AI. Additionally, litter size was standardised to 9 piglets/sow within 24 h of farrowing, with piglets receiving only maternal milk as their feed source. After weaning, sows were group-housed (3 sows/group), and boar exposure commenced on the 4th day after weaning (15 min of full), physical boar contact in a detection mating area at approximately 0900. At the first estrus after weaning, sows were AI twice, once in the afternoon following detection of first estrus and again approximately 18 h later at 1000 the following day. All AI took place in the detection mating area, with fence-line contact with a boar during the procedure. Inseminations were performed using disposable spirette catheters, with each AI consisting of an 80-ml dose (3 × 109 spermatozoa) of fresh (≤4 d old) extended semen of Large White and Landrace boars purchased from SABOR Pty., Ltd. (Clare, South Australia). 2.3. Animal measurements 2.3.1. Liveweight, body composition and reproductive parameters On d 1, 14 and 20 of lactation, sows were weighed before feeding and P2 backfat was measured over the last rib (65 mm ventral to the vertebrae) with an Ausonics Impact Ultrasound machine equipped with a 3.5 mHz linear array probe (Ausonics International Pty., Ltd., Camperdown, New South Wales, Australia). Piglets within each litter were also weighed on d 1, 13 and 20 of their dam’s lactation. In addition, post-weaning reproductive performance measures included the number of days from weaning to first estrus detection (weaning-to-estrus interval), the proportion of sows expressing estrus within 10 d of weaning, and subsequent (2nd) litter size. 2.3.2. Collection of milk samples On d 3, 13 and 20 of lactation, milk samples were collected approximately 30 min after litter removal, and immediately after a 2-mL i.m. injection of oxytocin (Troy Laboratories, Glendenning, NSW, Australia) from at least 6 teats (5 mL/teat). Milk fat and protein of each sow’s composite milk sample were measured by infrared spectroscopy (Bentley 2500 Combi; Bentley Instruments, Chaska, MN), calibrated before each assay with a standardized milk solution. Energy content (MJ/kg) was determined by multiplying concentrations of protein, fat and lactose by 0.0389, 0.0238, and 0.0164 MJ/g, respectively (Ramanau et al., 2004).
Please cite this article in press as: van Wettere, W.H.E.J., et al., Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance. Anim. Reprod. Sci. (2016), http://dx.doi.org/10.1016/j.anireprosci.2016.09.009
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W.H.E.J. van Wettere et al. / Animal Reproduction Science xxx (2016) xxx–xxx Table 2 Lactation liveweight (LW) and P2 backfat (P2) of first-parity sows fed a standard lactation diet (CTRL) or a lactation diet supplemented with ractopamine hydrochloride (RAC).a Treatment
Table 3 Liveweight (LW) and P2 backfat (P2) change during lactation of first-parity sows fed a standard lactation diet (CTRL) or a lactation diet supplemented with ractopamine hydrochloride (RAC).a
Pooled Across Treatment
CTRL
RAC
Number of sows
30
29
Sow LW (kg) D1 of lactation D14 of lactation D20 of lactation Pooled across day
176.4 ± 2.83 168.9 ± 2.74 164.7 ± 2.68 170.0 ± 1.69*
180.1 ± 3.17 174.7 ± 3.01 173.4 ± 2.88 176.1 ± 1.76*
178.3 ± 2.09c 171.8 ± 2.05b 169.1 ± 2.05a
Sow P2 (mm) D1 of lactation D14 of lactation D20 of lactation Pooled across day
21.2 ± 0.81 17.9 ± 0.85 17.3 ± 0.74 18.8 ± 0.51
21.1 ± 0.95 18.3 ± 0.81 18.5 ± 0.82 19.3 ± 0.52
21.1 ± 0.61b 18.1 ± 0.58a 17.9 ± 0.55a
abc superscripts within column, and variable, indicate significant difference; P < 0.05. * within row indicate differences at P < 0.1. a Ractopamine hydrochloride (Elanco Animal Health, Macquarie Park, Australia) was included at 10 mg/kg between d 1 and 13 of lactation and 20 mg/kg from d 14 of lactation to artificial insemination.
2.3.3. Statistical analysis Data were analyzed using a general linear mixed model (REML; Genstat software; Version 15; VSN International Ltd., Hemel Hempstead, UK). The model fitted differed depending on the variable, but in all cases sow was used as the experimental unit. Sow BW, P2 backfat and milk composition, as well as piglet BW were analyzed with treatment and day of measure fitted as fixed effects, and experimental block and sow included as random effects. Sow BW change and piglet growth rate were analyzed with treatment fitted as a fixed effect and sow and experimental block as a random effect. Weaning to oestrus interval and second litter size were analyzed with treatment fitted as a fixed effect and sow and experimental block as random effects. Means were statistically separated using the LSD option, with P ≤ 0.05 indicating a difference and P ≤ 0.10 indicative of a trend/tendency. In addition, chisquare analysis was used to test treatment differences for the proportion of sows expressing estrus within 10 d of weaning and subsequent farrowing rate. It should be noted that one sow was removed from the RAC treatment due to poor health; thus, data analysis included 30 CTRL- and 29 RAC sows. 3. Results 3.1. Sow body reserves, lactation feed intake and nutrient intake Even though sow weight were similar between CTRL and RAC sows on d 1 and 14 of lactation, RAC sows tended to be heavier (P = 0.07) on day 20 than CTRL-sows (Table 2). Regardless of day lactation, RAC sows tended (P < 0.1) to be heavier compared with CTRL-sows (Table 2). Moreover, BW loss between d 1 and 14 of lactation was similar between treatment groups; however, RAC-fed sows lost less (P < 0.05) BW between d 15 and 20 of lactation, and
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Lactation dietary treatment CTRL
RAC
Sow liveweight loss (kg) D 1–14 of lactation D 15–20 of lactation D 1–20 of lactation
7.3 ± 1.40 4.3 ± 0.98b 11.6 ± 2.08*
5.4 ± 1.63 1.3 ± 0.83a 6.8 ± 1.61*
Sow P2 backfat loss (mm) D 1–14 of lactation D 15–20 of lactation D 1–20 of lactation
3.0 ± 0.51 0.8 ± 0.34 3.7 ± 0.55*
2.2 ± 0.53 0.1 ± 0.35 2.3 ± 0.57*
ab
superscripts within row indicate significant difference; P < 0.05. P < 0.1. a Ractopamine hydrochloride (Elanco Animal Health, Macquarie Park, Australia) was included at 10 mg/kg between d 1 and 13 of lactation and 20 mg/kg from d 14 of lactation to artificial insemination. *
Table 4 Litter variables of first-parity sows fed a standard lactation diet (CTRL) or a lactation diet supplemented with ractopamine hydrochloride (RAC).a Lactation dietary treatment
Piglet growth rate (g/day) D 1–7 of lactation D 8–13 of lactation D 14–20 of lactation D 1–20 of lactation Piglet LW on day 20 lactation
Control
Ractopamine
200 ± 3.8 246 ± 3.5 295 ± 6.9b 243 ± 3.1b 6.3 ± 0.07b
203 ± 3.7 246 ± 3.4 255 ± 6.3a 232 ± 2.9a 6.1 ± 0.06a
ab
superscripts within row indicate significant difference; P < 0.01. Ractopamine hydrochloride (Elanco Animal Health, Macquarie Park, Australia) was included at 10 mg/kg between d 1 and 13 of lactation and 20 mg/kg from d 14 of lactation to artificial insemination. a
tended (P < 0.1) to lose more BWacross the entire 20-d lactation period, than CTRL-fed sows (Table 3). The proportion of BW loss in relation to initial (d 1) weight was less (P < 0.05) for sows fed RAC than CTRL (3.4 ± 0.01% versus 6.6 ± 0.01%). Furthermore, P2 backfat depth did not differ between CTRL- and RAC-fed sows on d1, 14, or 20 of lactation, and, although P2 backfat losses were similar between d 1 and 14 of lactation and d 15 to 20 of lactation, there was a tendency (P < 0.1) for RAC-sows to lose less backfat than CTRL- sows across the entire 20-d lactation period (Table 3). Additionally average daily feed intake (ADFI) did not differ between CTRL- and RAC-fed sows between d 1 to 14 of lactation (4.3 ± 0.08 and 4.3 ± 0.08 kg/d), d 14 to 20 (6.4 ± 0.13 and 6.3 ± 0.13 kg/d), or across the entire lactation period (5.2 ± 0.09 and 5.2 ± 0.09 kg/d). Regardless of treatment, day of lactation affected both sow BW and P2 backfat (Table 2). 3.2. Piglet growth characteristics Piglet average daily liveweight gain (ADG) was not affected by maternal dietary treatment between d 1–7 or d 7 to 13 of lactation (Table 4). However, ADG over the last 7 d before weaning (d 13 to 20) and over the entire 20-d lactation period was greater (P < 0.01) in piglets nursing CTRL-fed than RAC-fed sows (Table 4). Consequently,
Please cite this article in press as: van Wettere, W.H.E.J., et al., Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance. Anim. Reprod. Sci. (2016), http://dx.doi.org/10.1016/j.anireprosci.2016.09.009
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Table 5 Milk fat, protein, lactose and calculated energy contents on d 3, 13 and 20 of lactation of first-parity sows fed a standard lactation diet (CTRL) or a lactation diet supplemented with ractopamine hydrochloride (RAC).a Day of lactation
Pooled across day
Day 3
Day 13
Day 20
Fat (g/kg) Control Ractopamine
69.2 ± 1.75c 80.4 ± 2.54d
65.8 ± 1.84c 65.0 ± 1.56c
66.1 ± 2.35c 66.1 ± 2.03c
67.0 ± 1.15* 70.5 ± 1.90*
Protein (g/kg) Control Ractopamine
45.2 ± 0.72 45.7 ± 0.67
41.6 ± 0.54 39.1 ± 0.86
41.5 ± 0.50 40.0 ± 1.24
42.8 ± 0.33* 41.6 ± 0.62*
Lactose (g/kg) Control Ractopamine
57.0 ± 0.31 56.3 ± 0.48
59.8 ± 0.39 59.8 ± 0.38
59.2 ± 0.46 58.7 ± 0.87
58.6 ± 0.26 58.3 ± 0.37
Energy (MJ/kg) Control Ractopamine
4.3 ± 0.04c 4.6 ± 0.07d
4.2 ± 0.09c 4.1 ± 0.05c
4.2 ± 0.06c 4.1 ± 0.15c
4.2 ± 0.03 4.3 ± 0.06
cd
different superscripts indicate significant interaction between day of lactation and dietary treatment. within column, P < 0.06. Ractopamine hydrochloride (Elanco Animal Health, Macquarie Park, Australia) was included at 10 mg/kg between d 1 and 13 of lactation and 20 mg/kg from d 14 of lactation to artificial insemination. *
a
at weaning, piglets nursing CTRL-fed sows were heavier (P < 0.01) than piglets nursing RAC-fed sows. 3.3. Milk composition Milk samples from RAC-fed sows tended to have a greater (P = 0.06) concentration of fat, but a lesser (P = 0.06) concentration of protein, than milk from CTRL-fed sows (Table 5). Conversely, neither milk lactose content nor calculated energy content differed between the dietary treatments. Milk fat and protein content were higher (P < 0.05) on d 3 of lactation compared to d 13 and 20: 74.8 ± 1.70 versus 65.4 ± 1.25 and 66.1 ± 2.29 g fat/kg milk; 45.5 ± 0.40 versus 40.3 ± 0.49 and 40.8 ± 0.66 g protein/kg milk. Lactose levels were lower (P <0.05) on d 3 compared to d 13 and 20 of lactation (56.7 ± 0.29 versus 59.8 ± 0.27 and 59.0 ± 0.44 g lactose/kg milk) and energy levels were higher (P <0.05) on d 3 compared to d 13 and 20 of lactation (4.5 ± 0.04 versus 4.1 ± 0.03 and 4.1 ± 0.07 MJ/kg milk). 3.4. Sow reproductive performance The weaning to oestrus interval was similar for CTRL and RAC-fed sows. However, the proportion of CTRL sows exhibiting estrus within 10 d of weaning tended to be less (P = 0.07) than that of RAC sows (Table 6). The proportion of weaned sows which farrowed a second litter was 0.70 and 0.86 for the CTRL and RAC treatments. There was no effect of maternal dietary treatment on the percentage of sows mated or total number of piglets born in the 2nd litter (Table 6), but there was a tendency for the number of piglets born alive in the second litter to be greater (P = 0.06) in RAC-fed sows compared to CTRL-fed (Table 6). 4. Discussion Consistent with previous reports in the literature (Clowes et al., 2003; Thacker and Bilkei, 2005; Hoving et al., 2012), sows in the present study mobilized body reserves
during lactation, presumably to compensate for the deficit between recorded energy and lysine intakes and requirements for milk production. However, in the absence of any effect on ADFI, and, therefore intake of ME and lysine, RAC supplementation elicited a 49 and 38% reduction in the amount of BW and P2 backfat lost, respectively, during lactation. More specifically, RAC supplementation reduced lactation BW loss from 6.6% to 3.4% of initial (d 1) BW, and it was this conservation of maternal body reserves which was likely the cause of the improved reproduction observed in RAC-fed sows. Thacker and Bilkei (2005) demonstrated extended weaning to oestrus intervals in parity one sows with a lactation BW loss in excess of 5%. Consistent with this, RAC supplementation tended to increase the proportion of sows returning to estrus within 10 d of weaning. The tendency for second litter size to be improved in RAC supplemented sows should be treated with caution due to the small number of animals involved, and the relatively low litter size in the control sows. However results of this study were consistent with previous evidence that reducing sow BW loss during lactation increased ovarian follicle development and oocyte quality at weaning (Zak et al., 1997; Clowes et al., 2003), and increased both embryo survival (Hoving et al., 2012) and subsequent litter size (Thacker and Bilkei, 2005). In the present study, milk represented the sole source of nutrients for the nursing pigs, therefore, it can be assumed that observed differences in ADG of piglets nursing RAC-fed compared to CTRL-fed sows reflected alterations in either the nutritional quality or volume of the milk expressed by the sow. Milk yield is determined by a number of factors, including the number of pigs nursing the sow (Kim and Easter, 2001), and BW and body composition of the sow (Revell et al., 1998; Clowes et al., 2003) as well as dietary lysine and ME intakes (Noblet and Etienne, 1986; King et al., 1993). In the current study, these variables were kept constant such that the observed differences in sow and piglet performance could be attributed to the presence of RAC in the maternal diet.
Please cite this article in press as: van Wettere, W.H.E.J., et al., Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance. Anim. Reprod. Sci. (2016), http://dx.doi.org/10.1016/j.anireprosci.2016.09.009
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Table 6 Reproductive performance and second litter size of first-parity sows fed a standard lactation diet (CTRL) or a lactation diet supplemented with ractopamine hydrochloride (RAC).a Lactation dietary treatment Control
Ractopamine
Weaning to oestrus interval, days† Proportion sows oestrus by day 10 post-weaning
5.3 ± 0.35 0.77#
5.5 ± 0.34 0.93#
Sows farrowing a second litter as a: Proportion of sows weaned Proportion of sows mated
0.70 0.91
0.86 0.93
Second litter size Total born Born alive
8.41 ± 0.66 8.03 ± 0.61*
9.95 ± 0.68 9.73 ± 0.62*
#
P = 0.1 (2 = 3.08). P = 0.07. † Only sows exhibiting oestrus within 10 d of weaning. a Ractopamine hydrochloride (Elanco Animal Health, Macquarie Park, Australia) was included at 10 mg/kg between d 1 and 13 of lactation and 20 mg/kg from d 14 of lactation to artificial insemination. *
In primiparous sows, the nutrients for milk production come from either the diet or catabolism of maternal tissues, making it difficult to alter either yield or composition by manipulating sow body composition or protein intake (Revell et al., 1998). In contrast, maternal RAC supplementation stimulated a transient increase in milk fat in early lactation and a decrease in milk protein. In the current study dietary intake of AA and ME was similar across both treatments, suggesting that RAC may have decreased the contribution to milk production normally provided by the catabolism of maternal body reserves. From the current results it cannot be determined whether the reduced BW gain of pigs nursing RAC-fed sows reflected the observed decrease in milk protein or was indicative of a decrease in milk volume. Regardless, the ability of RAC to reduce maternal weight loss, in conjunction with a reduction in milk protein concentration, is consistent with the hypothesis that RAC effectively decreases protein degradation (Bell et al., 1998). The reduction in lactating sow BW loss, despite only a marginal reduction in P2 backfat, is consistent with the results from extensive studies in finishing pigs. Specifically, RAC has a limited capacity to affect lipogenesis or lipolysis primarily due to tissue insensitivity and rapid receptor down regulation (Mills et al., 1990; Liu et al., 1994; Dunshea and King, 1995). Interestingly, using circulating levels of NEFA as a marker of lipolysis, it appears that a transient increase in fat mobilization occurs in response to RAC feeding in limit-fed pigs, with NEFA levels returning to normal after 8 d of RAC feeding (Hancock and Anderson, 1990). As is normal practice, sows in the current study were on a relatively low feeding level immediately postpartum; thus, it is suggested that the currently observed increase in milk fat may have resulted from a transient increase in lipolysis in RAC-fed sows. The rapid desensitization of adipose tissue to -adrenergic receptors (Mills et al., 1990; Dunshea et al., 1993) may explain why milk fat levels were similar in RAC-fed and CTRL-fed sows over the last 7 d of lactation. It is evident that skeletal muscle protein is very sensitive to RAC administration, with the majority of studies demonstrating increased lean deposition and lean carcass content when growing pigs were fed diets formulated with RAC
(Bell et al., 1998; Apple et al., 2007). Increases in protein synthesis, in combination with reduced AA catabolism, are responsible for the increased protein deposition observed in response to RAC (Dunshea and King, 1994). Plasma urea concentrations are lower in RAC-fed finishing pigs (Dunshea and King, 1994). In the current study milk protein levels were reduced by RAC, indicating a reduction in AA availability for milk synthesis. Revell et al. (1998) suggested that dietary supplies of milk precursors, as opposed to maternal sources, become increasingly important for milk yield as lactation progresses. This may explain the capacity of RAC to inhibit BW loss appeared greater in later lactation, with dietary protein being increasingly directed to, and conserved in, skeletal protein. Alternatively, it is possible that the increased dose of RAC provided during the last week of lactation may have increased the response. Higher RAC doses increased fat free lean in growing pigs (Apple et al., 2007). Regardless of the precise mechanism, it is evident that RAC supplementation elicited a reduction in maternal tissue catabolism during lactation. It is also interesting that RAC promoted conservation of body reserves in sows suckling small litters (9 piglets), and it could be suggested this response to RAC may be higher in more prolific sows suckling larger litters. In conclusion, it is clear from the current results that adding RAC to the diets of lactating sows is an effective strategy to reduce mobilization of body reserves during lactation, particularly if feed intake is limited during lactation. It is also evident that the curtailed reduction in BW loss was sufficient to improve subsequent reproductive performance. The only negative associated with this strategy may be reductions in the ADG of pigs nursing RAC-fed sows, resulting in a 200 g (3.7%) reduction in pig weaning weight. Consequently, further work is being conducted to determine whether altering RAC inclusion dosage and provision of creep feed can alleviate this problem. The support for this study was provided by the CRC for an Internationally Competitive Pork Industry, and is gratefully acknowledged.
Please cite this article in press as: van Wettere, W.H.E.J., et al., Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance. Anim. Reprod. Sci. (2016), http://dx.doi.org/10.1016/j.anireprosci.2016.09.009
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References Apple, J.K., Rincker, P.J., McKeith, F.K., Carr, S.N., Armstrong, T.A., Matzat, P.D., 2007. Review: meta-analysis of the ractopamine response in finishing swine. Prof. Anim. Sci. 23, 179–196. Bell, A.W., Bauman, D.E., Beermann, D.H., Harrell, R.J., 1998. Nutrition, development and efficacy of growth modifiers in livestock species. J. Nutr. 128, 360S–363S. Clowes, E.J., Williams, I.H., Baracos, V.E., Pluske, J.R., Cegielski, A.C., Zak, L.J., Aherne, F.X., 1998. Feeding lactating primiparous sows to establish three divergent metabolic states: II: Effect on nitrogen partitioning and skeletal muscle composition. J. Anim. Sci. 76, 1154–1164. Clowes, E.J., Aherne, F.X., Foxcroft, G.R., Baracos, V.E., 2003. Selective protein loss in lactating sows is associated with reduced litter growth and ovarian function. J. Anim. Sci. 81, 753–764. Clowes, E.J., Aherne, F.X., Baracos, V.E., 2005. Skeletal muscle protein mobilisation during the progression of lactation. Am. J. Physiol. Endocrinol. Metab. 288, E564–E572. Dunshea, F.R., King, R.H., 1994. Temporal response of plasma metabolites to ractopamine treatment in the growing pig. Aust. J. Agric. Res. 45, 1683–1692. Dunshea, F.R., King, R.H., 1995. Responses to homeostatic signals in ractopamine-treated pigs. Br. J. Nutr. 73, 809–818. Dunshea, F.R., King, R.H., Campbell, R.G., Sainz, R.D., Kim, Y.S., 1993. Interrelationships between sex and ractopamine on protein and lipid deposition in rapidly growing pigs. J. Anim. Sci. 71, 2919–2930. Einarsson, S., Rojkittikhun, T., 1993. Effect of nutrition on pregnant and lactating sows. J. Reprod. Fertil. Suppl. 48, 229–239. Hancock, D., Anderson, D., 1990. Temporal changes in nitrogen metabolism and hormone/metabolism profiles post-ractopamine administration in swine. FASEB J. 4, A505. Hoving, L.L., Soede, N.M., Feitsma, H., Kemp, B., 2012. Lactation weight loss in primiparous sows: consequences for embryo survival and progesterone and relations with metabolic profiles. Reprod. Dom. Anim. 47, 1009–1016. Hughes, P.E., Varley, M.A., 2003. Lifetime performance of the sow. In: Wiseman, J., Varley, M.A., Kemp, B. (Eds.), Perspectives in Pig Science. Nottingham University Press, Nottingham, pp. 333–355. Jones, D.B., Stahly, T.S., 1999. Impact of amino acid nutrition during lactation on body nutrient mobilization and milk nutrient output in primiparous sows. J. Anim. Sci. 77, 1513–1522. Kim, S.W., Easter, R.A., 2001. Nutrient mobilization from body tissues as influenced by litter size in lactating sows. J. Anim. Sci. 79, 2179–2186.
King, R.H., Toner, M.S., Dove, H., Atwood, C.S., Brown, W.G., 1993. The response of first-litter sows to dietary protein level during lactation. J. Anim. Sci. 71, 2457–2463. Liu, C.Y., Grant, A.L., Kim, K.-H., Ji, S.Q., Hancock, D.L., Anderson, D.B., Mills, S.E., 1994. Limitations of ractopamine to affect adipose tissue metabolism in swine. J. Anim. Sci. 72, 62–67. Mejia-Guadarrama, C.A., Pasquier, A., Dourmad, J.Y., Prunier, A., Quesnel, H., 2002. Protein (lysine) restriction in primiparous lactating sows: effects on metabolic state, somatotropic axis, and reproductive performance after weaning. J. Anim. Sci. 80, 3286–3300. Mills, S.E., Liu, C.Y., Gu, Y., Schinckel, A.P., 1990. Effects of ractopamine on adipose tissue metabolism and insulin binding in finishing hogs Interaction with genotype and slaughter weight. Dom. Anim. Endocrinol. 7, 251–264. Noblet, J., Etienne, M., 1986. Effect of energy level in lactating sows on yield and composition of milk and nutrient balance of piglets. J. Anim. Sci. 63, 1888–1896. Quesnel, H., Mejia-Guadarrama, C.A., Pasquier, A., Dourmad, J.Y., Prunier, A., 2005. Dietary protein restriction during lactation in primiparous sows with different live weights at farrowing: II. Consequences on reproductive performance and interactions with metabolic status. Reprod. Nutr. Dev. 45, 57–68. Ramanau, A., Kluge, H., Spilke, J., Eder, K., 2004. Supplementation of sows with L-carnitine during pregnancy and lactation improves growth of the piglets during the suckling period through increased milk production. J. Nutr. 134, 86–92. Revell, D.K., Williams, I.H., Mullan, B.P., Ranford, J.L., Smits, R.J., 1998. Body composition at farrowing and nutrition during lactation affect the performance of primiparous sows: II. Milk composition milk yield, and pig growth. J. Anim. Sci. 76, 1738–1743. Ross, K.A., Beaulieu, A.D., Merrill, J., Vessie, G., Patience, J.F., 2011. The impact of ractopamine hydrochloride on growth and metabolism, with special consideration of its role in nitrogen balance and water utilization in pork production. J. Anim. Sci. 89, 2243–2256. Thacker, M.Y.C., Bilkei, G., 2005. Lactation weight loss influences subsequent reproductive performance of sows. Anim. Reprod. Sci. 88, 309–318. Zak, L.J., Xu, X., Hardin, R.T., Foxcroft, G.R., 1997. Impact of different patterns of feed intake during lactation in the primiparous sow on follicular development and oocyte maturation. J. Reprod. Fertil. 110, 99–106.
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Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance W.H.E.J. van Wettere a,∗ , S.J. Pain b , P.E. Hughes c a b c
School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy SA 5371, Australia Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North 4442, New Zealand Pig and Poultry Production Institute, SA 5371, Australia
a r t i c l e
i n f o
Article history: Received 26 April 2016 Received in revised form 5 September 2016 Accepted 9 September 2016 Available online xxx Keywords: Lactation Piglet Reproduction Ractopamine Sow
a b s t r a c t Excessive mobilization of body reserves during lactation delays the return to reproductive function in weaned primiparous sows. This study tested the hypothesis that supplementing the lactation diets of first-parity sows with ractopamine hydrochloride would reduce maternal weight loss and improve subsequent reproductive performance. Gestating gilts were allocated to one of two treatment groups (n = 30 sows/treatment), with one group fed a standard lactation diet (2.5 g/Mcal LYS: DE) throughout lactation (CTRL), whereas the treatment group received the standard lactation diet supplemented with 10 mg/kg ractopamine hydrochloride (RAC) from d 1 to 13 of lactation and 20 mg/kg RAC from d 14 of lactation until artificial insemination (AI). Weaning occurred on d 21 of lactation, with AI occurring at the first post-weaning estrus. Compared to CTRL, RAC supplementation decreased (P < 0.05) liveweight loss between d 13 and 20 of lactation (4.3 ± 0.90 versus 1.3 ± 0.96 kg), and tended to increase (P = 0.06) the number of second litter piglets born alive (9.5 ± 0.52 versus 8.1 ± 0.74). Treatment (RAC versus CTRL) reduced milk protein levels on d 13 and 20 of lactation (P < 0.05), and piglet weight gain between d 13 and 20 of lactation (260 ± 0.01 versus 310 ± 0.01 g/day, P < 0.01). In conclusion, it is evident that dietary RAC altered milk composition and stimulated conservation of maternal body reserves during the third week of lactation, resulting in a beneficial effect on subsequent reproductive performance. © 2016 Elsevier B.V. All rights reserved.
1. Introduction High incidences of premature culling of sows reduce the productivity of the breeding herd and overall herd feedconversion efficiency. Reproductive failure, particularly after the first lactation, is the primary reason for culling primiparous sows (Hughes and Varley, 2003). The high
∗ Corresponding author. E-mail address: [email protected] (W.H.E.J. van Wettere).
milk yield of modern sow genotypes, combined with the innate reduction in appetite of primiparous sows, results in insufficient feed consumption during the first lactation to meet requirements for maintenance, milk production and body growth (Clowes et al., 1998). The resultant nutritional deficit stimulates the catabolism of body reserves (Clowes et al., 2005), with high levels of tissue mobilization, from both fat reserves and skeletal protein, a primary cause of the delay, or failure, of primiparous sows to return to reproductive function post-weaning (Einarsson and Rojkittikhun, 1993; Clowes et al., 2003). High levels of protein mobilization during the first lactation suppress activity
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Table 1 Composition of the standard lactation sow diet. Ingredient
Nutrient composition, calculated
Item
%
Nutrient
Quantity
Barley Wheat Peas Soyabean meal Meat meal Fish meal Tallow Choline chloride Lysine − HCL d, l-Methionine l-Threonine Mineral mix Salt Limestone
57.0 14.25 10.0 6.0 5.0 2.5 3.75 0.045 0.14 0.025 0.01 0.25 0.3 0.75
Dry matter, % MCal/kg DE Crude Protein, % Fat, % Fibre, % Calcium, % Lysine, % Available lysine, % Methionine, % Threonine, % Tryptophan, % Salt, % Sodium, % Choline, ppm
89.9 3.34 18.7 6.21 4.2 1.0 1.0 0.84 0.31 0.62 0.19 0.54 0.18 1318.3
of the hypothalamic-pituitary-ovarian axis (Quesnel et al., 2005), extends the weaning to estrus interval (Jones and Stahly, 1999) and reduces post-weaning ovulation rate (Mejia-Guadarrama et al., 2002). It is, therefore, reasonable to suggest that if protein mobilization during the first lactation can be reduced, or prevented, then subsequent reproductive performance will be improved and level of culling among primiparous sows will be reduced. The addition of ractopamine hydrochloride, a widely used adrenergic agonist, to the diet of finishing swine increases net protein accretion, most likely due to a combination of increased protein synthesis and decreased protein degradation (Bell et al., 1998; Ross et al., 2011). The current study tested the hypothesis that dietary inclusion of ractopamine during the first lactation would reduce mobilization of maternal body reserves and lactating sow weight loss, resulting in improvements in subsequent reproductive performance. 2. Materials and methods 2.1. Animals This experiment was conducted at the University of Adelaide’s Piggery, Roseworthy, South Australia, with approval from the animal ethics committee of The University of Adelaide. The experiment was conducted in 4 replicates, with the first 2 replicates conducted in spring and 2 more conducted in autumn/winter. 2.2. Experimental treatments, housing and feeding Gestating Large White gilts (n = 60) were weighed and P2 back fat was ultrasonically measured on day 110 of gestation. From day 110 of gestation until weaning, sows were housed in temperature controlled farrowing accommodation, with a temperature range of 17 to 24◦C. Gilts were blocked by body weight (BW) and P2 backfat and allocated to 1 of 2 lactation treatment groups (n = 30 sows/treatment): first-parity sows that were fed a standard lactation diet (CTRL; 3.34 Mcal/kg DE, 18.7%CP, 6.2% crude fat, 4.2% crude fibre, and 2.5 g/Mcal LYS:DE; Table 1) throughout lactation and during the period from wean-
ing to artificial insemination (AI). The other first-parity sows received the same standard lactation diet supplemented with 10 mg/kg ractopamine hydrochloride (RAC; Elanco Animal Health, Macquarie Park, Australia) from days 1–13 of lactation and 20 mg/kg RAC day 14 of lactation until AI. Treatments began 24 h postpartum (designated as d0). During lactation, the amount of feed offered each day was stepped-up gradually, reaching a maximum offered of 6 kg/day the 4th d of lactation (3 meals/d), and daily feed disappearance was recorded for each sow. Pigs were weaned at 21 d of age, and all sows received 3 kg/day of their treatment diets between weaning and AI. Additionally, litter size was standardised to 9 piglets/sow within 24 h of farrowing, with piglets receiving only maternal milk as their feed source. After weaning, sows were group-housed (3 sows/group), and boar exposure commenced on the 4th day after weaning (15 min of full), physical boar contact in a detection mating area at approximately 0900. At the first estrus after weaning, sows were AI twice, once in the afternoon following detection of first estrus and again approximately 18 h later at 1000 the following day. All AI took place in the detection mating area, with fence-line contact with a boar during the procedure. Inseminations were performed using disposable spirette catheters, with each AI consisting of an 80-ml dose (3 × 109 spermatozoa) of fresh (≤4 d old) extended semen of Large White and Landrace boars purchased from SABOR Pty., Ltd. (Clare, South Australia). 2.3. Animal measurements 2.3.1. Liveweight, body composition and reproductive parameters On d 1, 14 and 20 of lactation, sows were weighed before feeding and P2 backfat was measured over the last rib (65 mm ventral to the vertebrae) with an Ausonics Impact Ultrasound machine equipped with a 3.5 mHz linear array probe (Ausonics International Pty., Ltd., Camperdown, New South Wales, Australia). Piglets within each litter were also weighed on d 1, 13 and 20 of their dam’s lactation. In addition, post-weaning reproductive performance measures included the number of days from weaning to first estrus detection (weaning-to-estrus interval), the proportion of sows expressing estrus within 10 d of weaning, and subsequent (2nd) litter size. 2.3.2. Collection of milk samples On d 3, 13 and 20 of lactation, milk samples were collected approximately 30 min after litter removal, and immediately after a 2-mL i.m. injection of oxytocin (Troy Laboratories, Glendenning, NSW, Australia) from at least 6 teats (5 mL/teat). Milk fat and protein of each sow’s composite milk sample were measured by infrared spectroscopy (Bentley 2500 Combi; Bentley Instruments, Chaska, MN), calibrated before each assay with a standardized milk solution. Energy content (MJ/kg) was determined by multiplying concentrations of protein, fat and lactose by 0.0389, 0.0238, and 0.0164 MJ/g, respectively (Ramanau et al., 2004).
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Table 3 Liveweight (LW) and P2 backfat (P2) change during lactation of first-parity sows fed a standard lactation diet (CTRL) or a lactation diet supplemented with ractopamine hydrochloride (RAC).a
Pooled Across Treatment
CTRL
RAC
Number of sows
30
29
Sow LW (kg) D1 of lactation D14 of lactation D20 of lactation Pooled across day
176.4 ± 2.83 168.9 ± 2.74 164.7 ± 2.68 170.0 ± 1.69*
180.1 ± 3.17 174.7 ± 3.01 173.4 ± 2.88 176.1 ± 1.76*
178.3 ± 2.09c 171.8 ± 2.05b 169.1 ± 2.05a
Sow P2 (mm) D1 of lactation D14 of lactation D20 of lactation Pooled across day
21.2 ± 0.81 17.9 ± 0.85 17.3 ± 0.74 18.8 ± 0.51
21.1 ± 0.95 18.3 ± 0.81 18.5 ± 0.82 19.3 ± 0.52
21.1 ± 0.61b 18.1 ± 0.58a 17.9 ± 0.55a
abc superscripts within column, and variable, indicate significant difference; P < 0.05. * within row indicate differences at P < 0.1. a Ractopamine hydrochloride (Elanco Animal Health, Macquarie Park, Australia) was included at 10 mg/kg between d 1 and 13 of lactation and 20 mg/kg from d 14 of lactation to artificial insemination.
2.3.3. Statistical analysis Data were analyzed using a general linear mixed model (REML; Genstat software; Version 15; VSN International Ltd., Hemel Hempstead, UK). The model fitted differed depending on the variable, but in all cases sow was used as the experimental unit. Sow BW, P2 backfat and milk composition, as well as piglet BW were analyzed with treatment and day of measure fitted as fixed effects, and experimental block and sow included as random effects. Sow BW change and piglet growth rate were analyzed with treatment fitted as a fixed effect and sow and experimental block as a random effect. Weaning to oestrus interval and second litter size were analyzed with treatment fitted as a fixed effect and sow and experimental block as random effects. Means were statistically separated using the LSD option, with P ≤ 0.05 indicating a difference and P ≤ 0.10 indicative of a trend/tendency. In addition, chisquare analysis was used to test treatment differences for the proportion of sows expressing estrus within 10 d of weaning and subsequent farrowing rate. It should be noted that one sow was removed from the RAC treatment due to poor health; thus, data analysis included 30 CTRL- and 29 RAC sows. 3. Results 3.1. Sow body reserves, lactation feed intake and nutrient intake Even though sow weight were similar between CTRL and RAC sows on d 1 and 14 of lactation, RAC sows tended to be heavier (P = 0.07) on day 20 than CTRL-sows (Table 2). Regardless of day lactation, RAC sows tended (P < 0.1) to be heavier compared with CTRL-sows (Table 2). Moreover, BW loss between d 1 and 14 of lactation was similar between treatment groups; however, RAC-fed sows lost less (P < 0.05) BW between d 15 and 20 of lactation, and
3
Lactation dietary treatment CTRL
RAC
Sow liveweight loss (kg) D 1–14 of lactation D 15–20 of lactation D 1–20 of lactation
7.3 ± 1.40 4.3 ± 0.98b 11.6 ± 2.08*
5.4 ± 1.63 1.3 ± 0.83a 6.8 ± 1.61*
Sow P2 backfat loss (mm) D 1–14 of lactation D 15–20 of lactation D 1–20 of lactation
3.0 ± 0.51 0.8 ± 0.34 3.7 ± 0.55*
2.2 ± 0.53 0.1 ± 0.35 2.3 ± 0.57*
ab
superscripts within row indicate significant difference; P < 0.05. P < 0.1. a Ractopamine hydrochloride (Elanco Animal Health, Macquarie Park, Australia) was included at 10 mg/kg between d 1 and 13 of lactation and 20 mg/kg from d 14 of lactation to artificial insemination. *
Table 4 Litter variables of first-parity sows fed a standard lactation diet (CTRL) or a lactation diet supplemented with ractopamine hydrochloride (RAC).a Lactation dietary treatment
Piglet growth rate (g/day) D 1–7 of lactation D 8–13 of lactation D 14–20 of lactation D 1–20 of lactation Piglet LW on day 20 lactation
Control
Ractopamine
200 ± 3.8 246 ± 3.5 295 ± 6.9b 243 ± 3.1b 6.3 ± 0.07b
203 ± 3.7 246 ± 3.4 255 ± 6.3a 232 ± 2.9a 6.1 ± 0.06a
ab
superscripts within row indicate significant difference; P < 0.01. Ractopamine hydrochloride (Elanco Animal Health, Macquarie Park, Australia) was included at 10 mg/kg between d 1 and 13 of lactation and 20 mg/kg from d 14 of lactation to artificial insemination. a
tended (P < 0.1) to lose more BWacross the entire 20-d lactation period, than CTRL-fed sows (Table 3). The proportion of BW loss in relation to initial (d 1) weight was less (P < 0.05) for sows fed RAC than CTRL (3.4 ± 0.01% versus 6.6 ± 0.01%). Furthermore, P2 backfat depth did not differ between CTRL- and RAC-fed sows on d1, 14, or 20 of lactation, and, although P2 backfat losses were similar between d 1 and 14 of lactation and d 15 to 20 of lactation, there was a tendency (P < 0.1) for RAC-sows to lose less backfat than CTRL- sows across the entire 20-d lactation period (Table 3). Additionally average daily feed intake (ADFI) did not differ between CTRL- and RAC-fed sows between d 1 to 14 of lactation (4.3 ± 0.08 and 4.3 ± 0.08 kg/d), d 14 to 20 (6.4 ± 0.13 and 6.3 ± 0.13 kg/d), or across the entire lactation period (5.2 ± 0.09 and 5.2 ± 0.09 kg/d). Regardless of treatment, day of lactation affected both sow BW and P2 backfat (Table 2). 3.2. Piglet growth characteristics Piglet average daily liveweight gain (ADG) was not affected by maternal dietary treatment between d 1–7 or d 7 to 13 of lactation (Table 4). However, ADG over the last 7 d before weaning (d 13 to 20) and over the entire 20-d lactation period was greater (P < 0.01) in piglets nursing CTRL-fed than RAC-fed sows (Table 4). Consequently,
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Table 5 Milk fat, protein, lactose and calculated energy contents on d 3, 13 and 20 of lactation of first-parity sows fed a standard lactation diet (CTRL) or a lactation diet supplemented with ractopamine hydrochloride (RAC).a Day of lactation
Pooled across day
Day 3
Day 13
Day 20
Fat (g/kg) Control Ractopamine
69.2 ± 1.75c 80.4 ± 2.54d
65.8 ± 1.84c 65.0 ± 1.56c
66.1 ± 2.35c 66.1 ± 2.03c
67.0 ± 1.15* 70.5 ± 1.90*
Protein (g/kg) Control Ractopamine
45.2 ± 0.72 45.7 ± 0.67
41.6 ± 0.54 39.1 ± 0.86
41.5 ± 0.50 40.0 ± 1.24
42.8 ± 0.33* 41.6 ± 0.62*
Lactose (g/kg) Control Ractopamine
57.0 ± 0.31 56.3 ± 0.48
59.8 ± 0.39 59.8 ± 0.38
59.2 ± 0.46 58.7 ± 0.87
58.6 ± 0.26 58.3 ± 0.37
Energy (MJ/kg) Control Ractopamine
4.3 ± 0.04c 4.6 ± 0.07d
4.2 ± 0.09c 4.1 ± 0.05c
4.2 ± 0.06c 4.1 ± 0.15c
4.2 ± 0.03 4.3 ± 0.06
cd
different superscripts indicate significant interaction between day of lactation and dietary treatment. within column, P < 0.06. Ractopamine hydrochloride (Elanco Animal Health, Macquarie Park, Australia) was included at 10 mg/kg between d 1 and 13 of lactation and 20 mg/kg from d 14 of lactation to artificial insemination. *
a
at weaning, piglets nursing CTRL-fed sows were heavier (P < 0.01) than piglets nursing RAC-fed sows. 3.3. Milk composition Milk samples from RAC-fed sows tended to have a greater (P = 0.06) concentration of fat, but a lesser (P = 0.06) concentration of protein, than milk from CTRL-fed sows (Table 5). Conversely, neither milk lactose content nor calculated energy content differed between the dietary treatments. Milk fat and protein content were higher (P < 0.05) on d 3 of lactation compared to d 13 and 20: 74.8 ± 1.70 versus 65.4 ± 1.25 and 66.1 ± 2.29 g fat/kg milk; 45.5 ± 0.40 versus 40.3 ± 0.49 and 40.8 ± 0.66 g protein/kg milk. Lactose levels were lower (P <0.05) on d 3 compared to d 13 and 20 of lactation (56.7 ± 0.29 versus 59.8 ± 0.27 and 59.0 ± 0.44 g lactose/kg milk) and energy levels were higher (P <0.05) on d 3 compared to d 13 and 20 of lactation (4.5 ± 0.04 versus 4.1 ± 0.03 and 4.1 ± 0.07 MJ/kg milk). 3.4. Sow reproductive performance The weaning to oestrus interval was similar for CTRL and RAC-fed sows. However, the proportion of CTRL sows exhibiting estrus within 10 d of weaning tended to be less (P = 0.07) than that of RAC sows (Table 6). The proportion of weaned sows which farrowed a second litter was 0.70 and 0.86 for the CTRL and RAC treatments. There was no effect of maternal dietary treatment on the percentage of sows mated or total number of piglets born in the 2nd litter (Table 6), but there was a tendency for the number of piglets born alive in the second litter to be greater (P = 0.06) in RAC-fed sows compared to CTRL-fed (Table 6). 4. Discussion Consistent with previous reports in the literature (Clowes et al., 2003; Thacker and Bilkei, 2005; Hoving et al., 2012), sows in the present study mobilized body reserves
during lactation, presumably to compensate for the deficit between recorded energy and lysine intakes and requirements for milk production. However, in the absence of any effect on ADFI, and, therefore intake of ME and lysine, RAC supplementation elicited a 49 and 38% reduction in the amount of BW and P2 backfat lost, respectively, during lactation. More specifically, RAC supplementation reduced lactation BW loss from 6.6% to 3.4% of initial (d 1) BW, and it was this conservation of maternal body reserves which was likely the cause of the improved reproduction observed in RAC-fed sows. Thacker and Bilkei (2005) demonstrated extended weaning to oestrus intervals in parity one sows with a lactation BW loss in excess of 5%. Consistent with this, RAC supplementation tended to increase the proportion of sows returning to estrus within 10 d of weaning. The tendency for second litter size to be improved in RAC supplemented sows should be treated with caution due to the small number of animals involved, and the relatively low litter size in the control sows. However results of this study were consistent with previous evidence that reducing sow BW loss during lactation increased ovarian follicle development and oocyte quality at weaning (Zak et al., 1997; Clowes et al., 2003), and increased both embryo survival (Hoving et al., 2012) and subsequent litter size (Thacker and Bilkei, 2005). In the present study, milk represented the sole source of nutrients for the nursing pigs, therefore, it can be assumed that observed differences in ADG of piglets nursing RAC-fed compared to CTRL-fed sows reflected alterations in either the nutritional quality or volume of the milk expressed by the sow. Milk yield is determined by a number of factors, including the number of pigs nursing the sow (Kim and Easter, 2001), and BW and body composition of the sow (Revell et al., 1998; Clowes et al., 2003) as well as dietary lysine and ME intakes (Noblet and Etienne, 1986; King et al., 1993). In the current study, these variables were kept constant such that the observed differences in sow and piglet performance could be attributed to the presence of RAC in the maternal diet.
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Table 6 Reproductive performance and second litter size of first-parity sows fed a standard lactation diet (CTRL) or a lactation diet supplemented with ractopamine hydrochloride (RAC).a Lactation dietary treatment Control
Ractopamine
Weaning to oestrus interval, days† Proportion sows oestrus by day 10 post-weaning
5.3 ± 0.35 0.77#
5.5 ± 0.34 0.93#
Sows farrowing a second litter as a: Proportion of sows weaned Proportion of sows mated
0.70 0.91
0.86 0.93
Second litter size Total born Born alive
8.41 ± 0.66 8.03 ± 0.61*
9.95 ± 0.68 9.73 ± 0.62*
#
P = 0.1 (2 = 3.08). P = 0.07. † Only sows exhibiting oestrus within 10 d of weaning. a Ractopamine hydrochloride (Elanco Animal Health, Macquarie Park, Australia) was included at 10 mg/kg between d 1 and 13 of lactation and 20 mg/kg from d 14 of lactation to artificial insemination. *
In primiparous sows, the nutrients for milk production come from either the diet or catabolism of maternal tissues, making it difficult to alter either yield or composition by manipulating sow body composition or protein intake (Revell et al., 1998). In contrast, maternal RAC supplementation stimulated a transient increase in milk fat in early lactation and a decrease in milk protein. In the current study dietary intake of AA and ME was similar across both treatments, suggesting that RAC may have decreased the contribution to milk production normally provided by the catabolism of maternal body reserves. From the current results it cannot be determined whether the reduced BW gain of pigs nursing RAC-fed sows reflected the observed decrease in milk protein or was indicative of a decrease in milk volume. Regardless, the ability of RAC to reduce maternal weight loss, in conjunction with a reduction in milk protein concentration, is consistent with the hypothesis that RAC effectively decreases protein degradation (Bell et al., 1998). The reduction in lactating sow BW loss, despite only a marginal reduction in P2 backfat, is consistent with the results from extensive studies in finishing pigs. Specifically, RAC has a limited capacity to affect lipogenesis or lipolysis primarily due to tissue insensitivity and rapid receptor down regulation (Mills et al., 1990; Liu et al., 1994; Dunshea and King, 1995). Interestingly, using circulating levels of NEFA as a marker of lipolysis, it appears that a transient increase in fat mobilization occurs in response to RAC feeding in limit-fed pigs, with NEFA levels returning to normal after 8 d of RAC feeding (Hancock and Anderson, 1990). As is normal practice, sows in the current study were on a relatively low feeding level immediately postpartum; thus, it is suggested that the currently observed increase in milk fat may have resulted from a transient increase in lipolysis in RAC-fed sows. The rapid desensitization of adipose tissue to -adrenergic receptors (Mills et al., 1990; Dunshea et al., 1993) may explain why milk fat levels were similar in RAC-fed and CTRL-fed sows over the last 7 d of lactation. It is evident that skeletal muscle protein is very sensitive to RAC administration, with the majority of studies demonstrating increased lean deposition and lean carcass content when growing pigs were fed diets formulated with RAC
(Bell et al., 1998; Apple et al., 2007). Increases in protein synthesis, in combination with reduced AA catabolism, are responsible for the increased protein deposition observed in response to RAC (Dunshea and King, 1994). Plasma urea concentrations are lower in RAC-fed finishing pigs (Dunshea and King, 1994). In the current study milk protein levels were reduced by RAC, indicating a reduction in AA availability for milk synthesis. Revell et al. (1998) suggested that dietary supplies of milk precursors, as opposed to maternal sources, become increasingly important for milk yield as lactation progresses. This may explain the capacity of RAC to inhibit BW loss appeared greater in later lactation, with dietary protein being increasingly directed to, and conserved in, skeletal protein. Alternatively, it is possible that the increased dose of RAC provided during the last week of lactation may have increased the response. Higher RAC doses increased fat free lean in growing pigs (Apple et al., 2007). Regardless of the precise mechanism, it is evident that RAC supplementation elicited a reduction in maternal tissue catabolism during lactation. It is also interesting that RAC promoted conservation of body reserves in sows suckling small litters (9 piglets), and it could be suggested this response to RAC may be higher in more prolific sows suckling larger litters. In conclusion, it is clear from the current results that adding RAC to the diets of lactating sows is an effective strategy to reduce mobilization of body reserves during lactation, particularly if feed intake is limited during lactation. It is also evident that the curtailed reduction in BW loss was sufficient to improve subsequent reproductive performance. The only negative associated with this strategy may be reductions in the ADG of pigs nursing RAC-fed sows, resulting in a 200 g (3.7%) reduction in pig weaning weight. Consequently, further work is being conducted to determine whether altering RAC inclusion dosage and provision of creep feed can alleviate this problem. The support for this study was provided by the CRC for an Internationally Competitive Pork Industry, and is gratefully acknowledged.
Please cite this article in press as: van Wettere, W.H.E.J., et al., Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance. Anim. Reprod. Sci. (2016), http://dx.doi.org/10.1016/j.anireprosci.2016.09.009
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Please cite this article in press as: van Wettere, W.H.E.J., et al., Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance. Anim. Reprod. Sci. (2016), http://dx.doi.org/10.1016/j.anireprosci.2016.09.009