NUTRITION AND SOW PROLIFICACY

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1 NUTRITION AND SOW PROLIFICACY Timothy M. Fakler 1 James E. Pettigrew 2 Christof J. Rapp 1 1 PhD, Zinpro Corporation Eden Prairie, MN USA 2 PhD, Pettigrew Consulting Int I, LLC, Louisiana, MO USA 1 Introduction Due to the high cost and difficulty of producing and maintaining a reproductive female, feeding sows to maximize sow prolificacy has become increasingly important. Nutritionists, veterinarians and producers are exploring numerous options in an attempt to increase sow productivity. These include nutritional modifications of sow diets as well as genetic, management and husbandry changes in an attempt to maximize the performance of the reproductive females on a farm. This paper will focus on nutrition and nutritional modifications of sow diets as a means to improve sow prolificacy. 2 Metabolic Mechanisms It is clear that inadequate intake of energy and/or amino acids impairs reproductive performance. However, the biological mechanisms through which nutrition affects reproduction are open to speculation. There are basically two theories as to how these mechanisms function. The first holds that reproduction is impaired when body fat (or protein) content falls below some threshold value. The second suggests that the reproductive system responds to metabolic cues that reflect the current metabolic state of the animal. Unfortunately, most experimental designs utilized to study the nutrition of lactation sows confound the body composition at weaning with the metabolic state during lactation and this has made it difficult to determine which school of thought is correct. It is likely that both are valid, but we believe the second is more important than the first. In support of the first school of thought, den Hartog and van Kempen (1980) suggested that female pigs must have a threshold level of body fat in order to reproduce normally. Subsequent experiments from several locations showed that sows underfed during lactation had lower body fat and protein contents at weaning and had impaired reproductive performances. However, sows that had similar body composition at weaning had different reproductive performances if they arrive at their respective body compositions by different routes (Mullan and Williams, 1989). Those sows that were given a moderate feeding level during pregnancy and a high level during lactation had shorter weaning to estrus intervals than did sows that were given a high feed intake level during pregnancy followed by a low level during lactation. In agreement, Xue et al. (1997) found that sows that were fat because they were overfed during pregnancy actually secreted less luteinizing hormone (LH) during lactation and had longer weaning to estrus intervals than did sows that were fed a normal feed intake regime. Perhaps the reduced voluntary feed intake during lactation or the reduced 25

2 insulin secretion of the fat sows caused this response. In addition, the same group of researchers (Rozeboom et al., 1995) found the body fat content at which gilts reached puberty was not uniform, but varied over a wide range even within genetically similar animals. Therefore, the whole-animal data do not support the notion that nutritional effects on reproduction are mediated through body fat content alone. Our working hypothesis, based on the second school of thought, is that nutritional effects on reproduction are mediated through the metabolic state of the animal (Pettigrew and Tokach, 1993). The metabolic state is considered to be a blend of several components including circulating concentrations of energy metabolites and of metabolic hormones, tissue sensitivity to these hormones, tissue metabolic capacity, homeostasis, homeorhesis and other parameters. Some components of the metabolic state surely send information about the nutritional state of the animal to the reproductive system. Of the potential components, insulin concentration is widely considered to be an important signal to the reproductive system (Britt et al., 1988; Pettigrew and Tokach 1993; and Foxcroft et al., 1995). There is evidence that both the whole-body level (Matamoros et al., 1991; Tokach et al., 1992; and Koketsu et al., 1996a) and on the tissue level (Pettigrew and Tokach, 1993) that insulin is involved in reproduction. Other components of the metabolic state, including leptin (Steiner, 1996) and IGF-I (Pettigrew and Tokach, 1993) may also serve as signals to the reproductive system. The metabolic state of a sow may affect any of several reproductive organs, including the hypothalamus, pituitary, ovaries and uterus. A current hypothesis is that the metabolic state during early development of ovarian follicles may affect the quality of those follicles when they are mature. This proposed phenomenon has been called follicular memory or follicular imprinting (Foxcroft et al., 1995). 3 Energy Increasing feed intake of lactating primiparous sows by 1 kg/d (from 4.5 to 5.5 kg/d) increases the subsequent litter size from 10.2 to 11.2 (Aherne, 1994). Increasing energy intake during this critical stage of production also reduces the weaning to estrus interval (Koketsu et al., 1996b). It is not enough to achieve a high average intake during the entire lactation, but to have a high intake at all stages/times during lactation. Metabolic studies have shown a strong correlation between insulin level during early lactation and the frequency of LH release during late lactation (Tokach et al., 1992 and Steiner 1996). These same studies showed that sows that returned to estrus promptly after weaning had higher insulin concentrations during early lactation than did sows with a delay between weaning and estrus. These observations suggest that the metabolic state during early lactation may be especially important for good subsequent reproduction, observations that are consistent with the concept of follicular memory. High levels of feed intake during the first two weeks of lactation was found to be more important for stimulating a prompt return to estrus after weaning than was intake during the final (third) week in a survey of commercial farms (Koketsu et al., 1997). In addition, the same group (Koketsu et al., 1996a) found that energy restriction during any week of lactation was detrimental on both LH release and weaning to estrus intervals. Energy restriction during the first week was not more detrimental than restriction during late 26

3 lactation. Zak et al. (1997) found that restriction during either the first three weeks of the only the fourth week of a 4 week lactation reduced ovulation rate at the first post-weaning estrus. However, restriction during the fourth week had an additional detrimental effect on embryo survival. The source of energy may also be important in determining the effects of energy on reproductive performance. The pancreas releases insulin in response a rise in blood glucose that results from the absorption of glucose release by starch digestion. Dietary fat does not produce glucose for absorption, so it may not stimulate insulin release to the same extent that dietary starch does. Therefore, substituting fat for starch in the diet of lactating sows may be detrimental to subsequent reproductive performance. This is an important issue, because many pork producers add fat to lactation diets in an effort to increase energy intake. Kemp et al. (1995) confirmed that serum insulin concentrations were lower in sows fed a diet containing fat, although the difference between treatments was limited to a short post-prandial period. This reduction in insulin response was associated with a small impairment of LH release. These results support the hypothesis that substituting fat for starch may be detrimental, although the effect appears to be subtle. The lack of response in this and other experiments (Lorschy et al., 1997) shows that there are unlikely to be large detrimental effects of fat supplementation of diets for lactations sows in commercial production on their subsequent prolificacy. In practice, we do not recommend against fat supplementation of lactating sow diets. In fact, we encourage fat supplementation for heat-stressed sows. Remember, fat supplementation of lactating sow diets has been shown to increase weaning weights (Pettigrew and Moser, 1991). High levels of dietary fiber may also improve reproductive performance (Ewan et al., 1996). In most research on fiber usage in sow diets, the fibrous diets have been fed during gestation, when nutrient requirements are low and feed restriction is common. We currently recommend avoiding high fiber levels during lactation to prevent the resulting reduction in digestible energy intake. 4 Amino Acids Lysine is the first limiting amino acid in lactating sow diets. Traditional input-output methods have been used to estimate the amount of dietary lysine needed to support a target litter growth rate. The question still remains as to whether a sow needs a higher dietary lysine level to maximize prolificacy. Recent data from Australia showed that increasing lysine content of the diet for primiparous sows during lactation to about 1.3% caused a large increase in subsequent litter size (Triton et al., 1996). Other recent work has shown that weaning to estrus intervals of primiparous sows on commercial farms was shortened by increasing dietary lysine intake above the level required to maximize litter weaning weight (Wilson et al., 1996). It is important still to estimate the level of dietary lysine needed to maximize both sow prolificacy and litter growth rates. Estimates of the daily lysine requirement of lactating sows to maximize litter growth range from 20 to more than 50 g (Pettigrew, 1993). At first glance, this appears to be a wide range and may be of little use in estimating the lysine requirement in practice. However, closer inspection of the data reveals that the experimental lysine requirement estimates relate closely to the litter 27

4 growth rates in the respective experiments. Regression of the lysine requirement estimates on the corresponding litter growth rates produced the following equation (Pettigrew, 1993): Apparent digestible lysine requirement (g/d) = (litter growth in g/d) Standard error of the estimate = 6.25: R 2 = 0.73 The slope (0.023) suggests that the sow needs 23 g of apparent digestible lysine for each kg of litter growth. The intercept (-7.36) suggests that the sow retrieves enough lysine from her body to meet the maintenance requirement plus reduces the dietary requirement by about 7 g/d. For example, to support milk production, a sow producing enough milk for a litter growth rate of 2 kg/d would need 39 g of apparent digestible lysine per day (46-7 = 39 g/d). If it is desired to provide enough lysine to eliminate the need for body protein mobilization to provide amino acids, the 7 g should not be subtracted, and the full 46 g/d should be provided to the sow. Note that 46 g of apparent digestible lysine corresponds to a total of 52 g of lysine in a corn-soy ration. Similar adjustments should be made for other feedstuffs based on apparent digestible lysine data. There is recent evidence that valine is required by lactating sows at much higher levels that was previously thought (Tokach et al., 1993; Richert et al., 1996). The pattern of response suggests that the sow responds to valine by increasing milk production, not by improving reproductive performance. Perhaps the higher requirement for valine is specific to the mammary glands. 5 Chromium Animal agriculture has shown recent interest in dietary chromium (Cr) due to reports of striking improvements in carcass quality of pigs (Lindemann et al., 1995a; Page et al., 1993; Smith et al., 1994; Boleman et al., 1995; Mooney and Cromwell, 1995); increased litter size in swine (Lindemann et al., 1995a); growth rate of turkeys (Steele and Rosebrough, 1981); and growth rate and immune response of stressed feeder calves (Chang and Mowat, 1992; Moonsie-Shageer and Mowat, 1993). Chromium is generally accepted as an essential nutrient that potentiates insulin action and thus influences carbohydrate, lipid and protein metabolism (Mertz, 1993). The specific biochemical function of Cr has not been clearly defined. The biologically active form of Cr, usually referred to as glucose tolerance factor (GTF), has been proposed to be a complex of Cr, nicotinic acid and possibly the amino acids glycine, cysteine and glutamic acid. Inorganic Cr compounds are poorly absorbed in animals (0.4 to 3.0%; Anderson, 1987) regardless of dose and dietary Cr status. In addition, Cr concentrations in common feedstuffs vary greatly. Little is known about the site or mechanism of absorption. An outgrowth of this recent interest, coupled with the poor absorption of inorganic Cr has led to the introduction of organic Cr sources that are being marketed as a more bioavailable source of Cr. 28

5 5.1 Chromium Metabolism Because Cr is associated with carbohydrate metabolism (Mertz, 1993), the metabolic effects of Cr supplementation may be demonstrated by investigating glucose metabolism. The Cr 3 + atom is thought to facilitate interactions between insulin and insulin receptors on target tissues such as muscle and fat. In this way, Cr potentiates anabolic activities of insulin. Insulin s main function is to regulate blood glucose levels. When bound to its receptor, insulin causes cellular uptake of glucose, thereby clearing it from the blood. Once acquired by cells, glucose is used as an energy source that, along with the anabolic actions of hormones such as growth hormone and IGF-I, drives protein synthesis, growth of lean tissue and proper maintenance and function of other organs. Biologically active Cr also aids in the conversion of thyroxine (T 4 ) to triiodothyronine (T 3 ) the thyroid hormone that increases metabolic rate causing increased oxygen consumption, heat production, metabolism of fats, proteins and carbohydrates, cardiac output and RNA and protein synthesis. The improvements in carcass quality in pigs may be due to this potentiation of insulin function. Steele et al. (1977) demonstrated that Cr as GTF increased insulin sensitivity in pigs. Amoikon et al. (1995) reported that dietary Cr as chromium picolinate increased glucose disappearance rate and decreased glucose half-life in growing pigs. Chromium supplementation in humans with mild hyperglycemia has been shown to improve glucose tolerance. In addition, Cr supplementation normalizes the levels of the metabolic hormones insulin and glucagon (Anderson et al., 1991). Chromium deficiency expresses itself as a general impairment in insulin sensitivity making it similar to type 2 or insulin resistant diabetes. When Cr is deficient, supplementation can improve glucose tolerance by increasing the insulin-stimulated uptake of glucose from the blood. Chromium supplementation can also enhance insulin action that results in reduced blood insulin levels since it takes less insulin to promote glucose uptake by tissues. 5.2 Chromium and Sow Reproductive Performance Recent research with bioavailable sources of Cr 3 + has shown that reproductive performance of sows could be improved with dietary supplementation. Lindemann et al. (1995a) reported that in gilts consuming diets supplemented with 200 ppb Cr as chromium picolinate, the number of pigs born live and weaned increased by 1.3 and 2.1 pigs per litter, respectively. In additional trials, Lindemann et al. (1995b) reported that in gilts supplemented with 200 ppb Cr as chromium picolinate from the time of first breeding, with continued supplementation through three parities, slight improvements in pigs born live were observed in the first parity (0.04 pigs per litter) and the magnitude of this effect increased with subsequent parities (0.7 pigs per litter and 2 pigs per litter in parity two and three, respectively). These data would indicate that the response of reproducing sows to supplemental Cr might be time dependent, with the magnitude of improvements in reproductive performance increasing as time period of supplementation increases. Campbell (1996) reported that supplementation of sow diets with 200 ppb Cr as chromium picolinate for one parity resulted in no significant improvements in litter size; however, farrowing rate of both first and second parity sows was improved (parity one 29

6 79 percent vs. 92 percent; parity two, 79 percent vs. 95 percent in non-supplemented vs. Cr supplemented sows, respectively). While these results are exciting, it is important to examine potential modes of action for increases in reproductive performance in sows supplemented with bioavailable Cr sources. Chromium as an element has been reported to be necessary for proper carbohydrate metabolism in man (Mertz, 1993), rats (Striffler, et al. 1993), and pigs (Amoikon, et al., 1995). Specifically, Cr has been reported to be a component of a metabolic complex termed GTF that potentiates the action of insulin potency by aiding the insulin/insulin-receptor interaction (Mertz, et al., 1995). Based on this knowledge, a hypothesis was put forth by Trout (1995) to explain the role of chromium reproductive performance. Insulin has been reported to have a positive effect on ovarian development, including a stimulatory effect on ovarian granulosa cell proliferation (Spicer and Echternkamp, 1995) and maturation (May and Schomberg, 1981; Amsterdam et al., 1988), and a decrease in follicular atresia (Matamoros et al., 1990) in sows. The percentage of medium follicles that became atretic decreased from 38.2 to 10.7 in control vs. insulin treated sows, respectively. Possibly as a result of this increased ovarian development, insulin has been reported to increase blood progesterone concentrations (Ciancio, 1984; Amsterdam et al., 1988; Clowes, et al., 1994; Kemp, et al., 1995). Channing et al. (1976) reported that in cultured porcine granulosa cells, insulin was necessary to bring about full luteinization and progestin production under the influence of FSH and LH. Progesterone is responsible for preparing the uterus for pregnancy and there appears to be a link between circulating progesterone concentrations and embryo survival (Pharazyn, et al., 1991; Jindal and Foxcroft, More recently, Garcia (1997) reported that circulating progesterone concentrations on day 13 of the reproductive cycle were unaffected by supplemental Cr despite the fact that insulin function was improved. However, uterine oxytocin levels were increased with increasing Cr. Additionally, natural and exogenous insulin have been reported to increase the ovulation rate in pigs (Flowers et al., 1989; Cox, et al., 1986, 1987). After treatment of gilts prior to estrus, ovulation rate was increased from 14.6 to 17.0 in control vs. treated animals. This effect may be the result of insulin affecting the release of LH at the level of the hypothalamus or the pituitary (Flowers et al., 1989). Adashi et al., (1981) reported that insulin improved the responsiveness of pituitary cells to GnRH and increased the basal and maximal release of LH and FSH in-vitro. Insulin treatment of gilts resulted in increased LH surges per 4-hour period on day 2 of the estrus cycle. Additionally, Cox et al. (1987) reported that insulin treatment in sows tended to increase circulating LH concentrations. Because it has been demonstrated that Cr potentiates insulin action, it was theorized that Cr might affect ovulation rate. Garcia et al. (1987) reported, in preliminary data, that ovulation rate was unaffected when assessed on day 13 of the estrous cycle in second cycle gilts fed supplemental Cr during development. Further research is necessary to identify the mode of action by which Cr increases litter size and farrowing rate. However, insulin may affect litter size by increasing ovulation rate and by increasing early embryo survival. If Cr potentiates the response of insulin, it may affect litter size by increasing ovulation rate and/or embryo survival. 30

7 5.3 Dietary Chromium-L-Methionine Supplementation Improves Sow Performance This study was conducted to evaluate the reproductive performance and changes in body composition in sows fed supplemental Cr from CrMet. One-hundred eighty-two sows (Landrace x Duroc) were housed individually in elevated farrowing crates in a naturally ventilated sow research facility in Queretaro, Mexico. Sows were moved from gestation stalls to the farrowing crates at d 109 of gestation and treatments were initiated. Sows were allotted to treatment based on current parity and assigned to one of three dietary treatments: Control, Control plus 200 ppb Cr from CrMet or Control plus 400 ppb Cr from CrMet. Treatments were applied to sows through lactation and up to re-breeding (up to 24 d post weaning). Piglets were weaned at 21 d of age. Sows were followed through to the next (subsequent) farrowing in order to determine the effect of added Cr on piglets farrowed in the subsequent litter. Sows fed chromium-l-methionine had more than one additional piglet per litter in the farrowing following treatment compared to control sows (P = 0.01). In addition, sows fed Cr tended to lose less weight and produce heavier piglets during the lactation period. Chromium supplementation of lactating and re-breeding sows induced greater prolificacy at the subsequent farrowing, perhaps, through improvement of insulin function. Other benefits in sow productivity and maintenance seem to be feed intake dependant and possibly dietary energy source and feed intake patterns are of importance in assuring clear effects. 6 Summary and Conclusions In practice, producers should avoid over feeding during gestation because fat sows eat less during lactation. Producers should avoid or minimize heat stress for sows. Heat stress reduces voluntary feed intake. Practices that can reduce heat stress include adequate ventilation, using a flooring material that conducts heat away from sows, drip cooling and snout cooling. Sows should be fed frequently (three to four times a day). Water intake is also very important. Producers should be certain to provide a clean, ample water supply. Cup waterers are preferred over nipples (if nipple waterers are used, ensure an adequate flow rate). Producers should avoid low energy (high fiber) diets during lactation. Nutrition clearly affects sow prolificacy. It appears that the connection between nutrition and subsequent reproductive performance is mediated through the metabolic state of the sow. This indicates that sows should be fed moderately during gestation so they will consume an adequate amount of feed during lactation. A high level of feed intake is important during each phase of lactation. It also appears that supplemental fat in the lactation diet has no large detrimental effect on prolificacy. The amount of lysine required to maximize litter growth rate can be estimated and should be utilized in production setting to determine the appropriate level of supplementation. Management practices to encourage a high level of feed intake during lactation should be encouraged. Chromium appears to improve sow prolificacy probably through its effect on insulin. 31

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