Consequences of nutrition and growth retardation early in life for growth and composition of cattle and eating quality of beef P.L. Greenwood1, L.M. Cafe1,2, H. Hearnshaw2 and D.W. Hennessy2 Cooperative Research Centre for Cattle and Beef Quality, University of New England, Armidale NSW 2351 1NSW Department of Primary Industries, Beef Industry Centre of Excellence, University of New England, Armidale NSW 2351, [email protected]
2Formerly, NSW Department of Primary Industries, Agricultural Research and Advisory Station, Grafton, NSW 2460
Summary Severe growth retardation of cattle early in life is associated with reduced growth potential, resulting in smaller animals at any given age. Growth potential diminishes as age of onset of nutritional restriction declines, and severe, prolonged intra–uterine growth retardation may result in slower growth of cattle throughout life. Severe weight loss during the months immediately after weaning or slow growth after early– weaning also limits compensatory growth. Carcass composition of small and large newborns is similar at heavier market weights. At equivalent weights, calves grown slowly to weaning subsequently have carcasses of similar or leaner composition than those grown rapidly, unless high energy concentrate feed is provided post–weaning, causing increased fatness. Adverse effects of early–life growth on eating quality at market weights are not evident. When differences occur, they suggest that cattle restricted early in life may have slightly more tender meat. We propose that within pasture–based systems, plasticity of carcass tissues, particularly muscle which maintains a stem cell population, allows cattle growth–retarded early in life to attain normal composition at equivalent weights in the long–term, albeit at older ages. However, nutrition during recovery or following early–weaning is important in determining the subsequent composition of young, light–weight cattle relative to heavier counterparts. Keywords: cattle, foetus, placenta, birth weight, growth, weaning, nutrition
Introduction In Australia, growth of cattle to market weights is typically a prolonged process subject to short– and long–term environmental variation. Most notably, cattle experience variable nutrition due to climatic extremes. Growth of the bovine foetus has well–studied consequences for survival, and can be slowed during the latter half of gestation by restricted nutrition and/or inadequate placental development. Similarly,
influences of pre–weaning nutrition on growth to market weights of cattle are well–characterised. However, consequences of foetal calf growth for subsequent growth and of foetal and neonatal calf growth for carcass characteristics of cattle are less well understood. This review focuses on research into consequences of cattle nutrition and growth early in life for subsequent growth and carcass composition of cattle and eating quality of beef. It includes initial findings from our recent studies on consequences of growth during pregnancy and to weaning of cattle sired by genotypes with extreme propensities for muscle and intramuscular fat development. Growth and nutrition of the bovine foetus and factors affecting it are also briefly discussed and, where instructive, results for sheep are also presented, as development has been extensively studied in this ruminant species.
Normal bovine conceptus growth and metabolism It is important to recognise that, unlike postnatal growth in which energy and nutrient availability influence growth and body composition of cattle directly, environmental influences on foetal growth and development, and hence birth characteristics, are regulated via the dam and the placenta, the nutritional conduit between dam and foetus. Most growth of the bovine foetus occurs during late gestation (Winters et al. 1942; Lyne 1960; Ferrell et al. 1976; Prior and Laster 1979). Foetal growth follows a flattened sigmoid pattern during the latter half of gestation as it proceeds from an early exponential phase through a rapid, linear phase, and then begins to diminish as term approaches (Greenwood and Bell 2003a, 2003b). Foetal nutrient uptake becomes a quantitatively important contributor to maternal nutrient requirements only after mid–gestation (Ferrell et al. 1983). Unlike the sheep, in which the placenta attains most of its mass of dry tissue, protein and DNA by mid–gestation (Ehrhardt
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and Bell 1995), the bovine placenta normally continues to increase in weight until near term (Prior and Laster 1979; Ferrell 1989). As a result, it has been suggested that placental growth may be less sensitive to nutritional deficiencies in cattle than in sheep. Placental weight and birth weight are highly correlated in cattle (Anthony et al. 1986b; Echternkamp 1993; Zhang et al. 1999), and the functional capacity of the placenta is closely related to placental perfusion. Bovine uterine and umbilical blood flow increases exponentially during the second half of gestation, which equates to relatively constant rates of umbilical blood flow on a foetal weight–specific basis during this period (Reynolds et al. 1986). Detailed accounts of placental function and metabolism are provided by Ferrell (1989) and Bell et al. (2005). Foetal mass increases many–fold from mid to late gestation and this increase is accompanied by increased rates of uterine and umbilical uptake of oxygen and nutrients, of urea export by conceptus tissues, and of foetal whole–body protein synthesis in cattle and sheep (Bell et al. 1986; Reynolds et al. 1986; Kennaugh et al. 1987; Bell et al. 1989; Ferrell 1991b). During late pregnancy in both of these species, 35–40% of foetal energy is taken up as glucose and its foetal–placental metabolite lactate, and a further 55% is taken up as free amino acids. In contrast to its importance as an energy source in the maternal ruminant, umbilical uptake of acetate is estimated to account for only 5–10% of foetal energy consumption. About 60% of amino acids are used for tissue protein synthesis, which accounts for approximately 18% of foetal energy expenditure (Kennaugh et al. 1987). The remaining 40% of amino acids are rapidly catabolised, accounting for at least 30% of the oxidative requirements in the well–nourished sheep foetus (Faichney and White 1987) or, in the case of glutamine and serine, are taken up and metabolized by the placenta (Battaglia and Regnault 2001).
Intrauterine growth retardation Maternal nutrition In cattle, severe nutritional restriction for at least the last half to one–third of pregnancy is usually required to reduce foetal growth. Significant reductions in birth weight were caused by prolonged underfeeding of heifers from weaning until parturition (Wiltbank et al. 1965), and underfeeding of heifers and cows during the second and third trimesters (Ryley and Gartner 1962; Hodge and Rowan 1970; Freetly et al. 2000; Hennessy et al. 2002) or during late pregnancy only (Hight, 1966; Tudor 1972; Bellows and Short 1978; Kroker and Cummins 1979). The effect of nutritional restriction on birth weight was more pronounced in heifers than cows when the period of restriction encompassed mid and late gestation (Hennessy et al. 2002) rather than late gestation only (Tudor 1972). However, birth weight was not significantly affected by nutritional restriction from mating to 140 days of gestation in heifers (Cooper et al.
1998), during the final 12 weeks of pregnancy (Hodge et al. 1976) in heifers or during the second trimester in mature cows (Freetly et al. 2000). Foetal growth capacity can interact with available nutrition in determining the extent to which foetal growth is retarded. Birth weight of calves of Hereford dams sired by double–muscled Piedmontese bulls was more affected by restricted nutrition during mid and late pregnancy than those sired by Wagyu bulls, and birth weight of male calves was affected more than that of female calves (Hennessy et al. 2002). When assessed within parity and sire–breed, nutritional restriction resulted in reduced birth weights of Piedmontese–sired calves from heifers and cows, but only of Wagyu–sired calves from heifers. Effects of foetal growth potential, or foetal nutrient demand, on the nutritional reserves of pregnant cows were also evident (Greenwood et al. 2002b). Dams mobilised more muscle to support growth of male than female foetuses and tended to mobilise more muscle to support growth of Piedmontese– than Wagyu–sired foetuses; while heifers mobilised less fat and muscle to support foetal growth than cows. During the final one–half to one–third of pregnancy, feed energy available to the dam appears to have more influence on birth weight than the availability of protein, although results are variable (Holland and Odde 1992). Variation in feed energy available to the dam during this period can result in differences in birth weight ranging from 0–8.2 kg (Dunn et al. 1969; Tudor 1972; Laster 1974; Corah et al. 1975; Bellows and Short 1978; Kroker and Cummins 1979; Bellows et al. 1982). Variable dietary protein supply during the third trimester may (Bellows et al.1978) or may not (Anthony et al. 1986a; Holland and Odde 1987) alter birth weight of calves, and restricted or supplemental dietary protein during early or mid pregnancy had little effect on birth weights (Perry et al. 1999, 2002). However, chronic restriction of energy supply to heifers from weaning until parturition resulted in birth weight differences of up to 10 kg and chronic restriction of protein supply over this period resulted in birth weight differences of up to 7.3 kg (Wiltbank et al. 1965). Placental weight and birth weight are highly correlated in cattle. However, because the bovine placenta may continue to increase in mass until near term, it is not clear whether the placenta regulates bovine foetal growth to the same extent as it does in sheep (Ferrell 1989). Placental characteristics may be altered by nutrition during early and mid pregnancy without significantly affecting foetal size (Rasby et al. 1990), and protein supplementation of cows during early or mid pregnancy may also alter placental characteristics without necessarily affecting birth weight (Perry et al.1999, 2002). Because development and growth of vital organs precedes development of bone, muscle and fat (Palsson 1955), respectively, the mass of the late maturing carcass tissues are generally considered more susceptible to the effects of nutrition during late pregnancy when it
Consequences of nutrition and growth of cattle early in life
impacts most on foetal growth. However, more subtle effects on organ and tissue development due to nutrition during early pregnancy may occur, with potential for long term consequences for health, as shown in sheep (Greenwood and Bell 2003a, 2003b; Bell et al. 2005).
Thermal environment Foetal growth in cattle can be restricted (18% lower foetal weight) by chronic heat stress of pregnant cows, and provision of shade resulted in a 3.1 kg increase in birth weight (Collier et al. 1982). Severe cold stress of cattle may also reduce foetal growth if inadequate nutrition is provided to meet metabolic requirements additional to foetal requirements for growth and development (Andreoli et al. 1988), but more moderate cold stress of sheep ewes in late gestation increased birth weight by 15% (Thompson et al. 1982). It is believed that temperature regulates blood flow to the periphery and lungs in order to preserve or dissipate body heat, resulting in increased or decreased blood flow and nutrient supply to the gravid uterus (Reynolds et al. 1985). In the sheep, chronic heat stress during early to mid gestation restricts placental development, thus imposing a limitation on subsequent foetal growth irrespective of nutrition later in pregnancy (Bell et al. 1987).
Parity Heifers give birth to smaller calves than cows (Holland and Odde 1992) because the size and nutritional requirements for growth of heifers limit nutrient availability for placental and foetal growth. Severe maternal nutritional restriction impacts more on birth weight of calves of heifers than of cows, particularly among male calves and those of sires with inherently high birth–weight offspring (Hennessy et al. 2002). In adolescent sheep fed to attain excessive fatness prior to and during gestation, placental and foetal growth and birth weight are reduced (Wallace et al. 1996, 1999).
Litter size Twin calves are rare in cattle unless exogenous regulation of ovarian function or embryo transfer is practiced. Individuals within litters have reduced foetal growth compared to singletons due to a reduced number of placentomes and mass of placenta per foetus (Hafez and Rajakoski 1964; Greenwood et al. 2000b) and because of greater total nutrient requirements of the litter. On average, twin calves are 7.4–9.8 kg lighter than singletons (Gregory et al. 1990, 1996; de Rose and Wilton 1991; Cummins 1994; Wilkins et al. 1994). Restricted nutrition limits foetal growth earlier and more severely in twins or higher multiples than in singletons, although stocking rates of pregnant cows fed pasture did not significantly influence twin birth weights (Wilkins et al. 1994).
Foetal and maternal genotype Foetal genotype is most important in determining foetal growth during early and mid pregnancy, whereas maternal genotype is more important in determining foetal growth during late pregnancy when most foetal growth normally occurs and foetal growth is increasingly subject to external influences mediated via the dam. The effect of foetal and maternal genotype on foetal growth was most convincingly demonstrated in cattle by Ferrell (1991a), who implanted Charolais (heavier birth weight) or Brahman (lighter birth weight) embryos into Charolais and Brahman cows. At 232 days of pregnancy, each foetal genotype was similar in size, irrespective of dam breed. However, by 274 days of gestation, Charolais foetuses in Brahman cows were 7 kg lighter than those in Charolais cows. In contrast, Brahman foetuses in Charolais cows were only 2 kg heavier than those in Brahman cows. Similar results were obtained by Joubert and Hammond (1958) for birth weights for South Devon and Dexter cattle and their reciprocal crosses.
Growth and development from birth to weaning Calves undergo a transition at birth from a diet comprising primarily glucose and amino acids to one which is quantitatively greater and is proportionately higher in fat. This is associated with maturation of the digestive, metabolic and endocrine systems. Evidence in sheep suggests severely growth–retarded newborns are immature with respect to energy metabolism and have more foetal–like metabolism than their well–grown counterparts (Rhoads et al. 2000a,b; Greenwood et al. 2002a). The major nutritional factors affecting pre– weaning calf growth and composition at weaning are lactational performance of the dam and quality and availability of nutrients from pasture and/or supplementation prior to and following parturition. Most notably, maternal genotype, age, parity, body condition and liveweight interact with calf growth capacity and milk consumption capacity to influence lactational output. Calves become increasingly dependent on forage–based diets, which result in the production of volatile fatty acids that stimulate development and maturation of the rumen (Warner and Flatt 1965). Early weaning is practiced primarily to allow the dam to recover body condition to maximise reproductive rates, particularly in harsher nutritional environments, or in high output or accelerated finishing systems. Successful weaning at a very young age requires adequate growth and rumen development by weaning, and usually involves access by young cattle of low liveweight to a high protein, high energy concentrate supplement prior to, during and after weaning because
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they have a higher requirement for protein relative to energy than their heavier counterparts (Leibholz 1971a,b).
Long–term consequences of altered growth during early life of cattle Consequences of foetal growth and nutrition Our recent studies have demonstrated that foetal growth restriction resulting in 10.2 kg or 26% lower birth weight (Table 1) may limit the capacity of cattle to exhibit compensatory growth. Cattle significantly growth–retarded during foetal life due to severely restricted maternal nutrition from day 80–90 of pregnancy until parturition remained smaller at any given postnatal age compared to their well–grown or better nourished counterparts (Table 1). Whether this represents a permanent stunting or simply a delay of attainment of mature size of cattle is open to conjecture. Growth of low birth weight cattle was significantly slower than that of high birth weight cattle at all stages of postnatal growth, although pre–weaning growth was likely to have been influenced by maternal nutritional status during pregnancy. Low birth–weight male calves reared rapidly to weaning grew faster than their high birth–weight counterparts during artificial rearing, whereas the opposite occurred for female calves (Tudor and O’Rourke 1980). Calves that had birth weights 5.4 kg and 5.9 kg lower than those from cows well–nourished during late pregnancy were 16.5 kg and 17.2 kg lighter at weaning (Hight 1966, 1968a). However, it should be noted that, in assessing influences of foetal development on postnatal performance, it is not possible to fully separate out consequences of nutrition during pregnancy on the foetus when offspring remain with their dams to weaning because of carry–over effects on
maternal performance (see Greenwood et al. 1998 for an example of a rearing system designed to uncouple prenatal and postnatal influences).Despite this, the net effects of maternal nutrition during pregnancy on the calf remain of practical significance to livestock producers. In this regard, differences in weight of calves at birth following three levels of maternal nutrition during late–pregnancy disappeared by weaning when postnatal nutrition was of high quality and availability, although residual effects of the previous year’s nutrition did influence calf growth (Hight 1968b). Similarly, effects of variable nutrition during mid and/or late pregnancy on weight at birth were overcome by adequate nutrition postpartum, resulting in no differences in body weight at 58 days of age (Freetly et al. 2000). Twin cattle are lighter at birth and grow more slowly until weaning when they remain with their dams (Hennessy and Wilkins 1997). Compared to singletons post–weaning, they may grow more slowly (Gregory et al. 1996), at a similar rate (de Rose and Wilton 1991), or more rapidly (Wilkins et al. 1994; Clarke et al. 1994; Hennessy and Wilkins 1997), depending upon the rearing system and subsequent nutritional regimen. However, twin cattle tended to consume less feed in the feedlot than singletons, mainly because of their lower liveweights (de Rose and Wilton 1991). Few studies examined the long–term consequences of foetal nutrition and growth for body and carcass characteristics in cattle (Tudor et al. 1980) prior our recent studies (Cafe et al. 2004a,b,c; Greenwood et al. 2004; Hearnshaw et al. 2004), but there have been an increasing number of studies with sheep (Villette and Theriez 1981; Nordby et al. 1987; Greenwood et al. 1998; Krausgrill et al. 1999; Oliver et al. 2001; Gopalakrishnan et al. 2004; Paganoni et al. 2004a,b), and there is increasing interest in the influence of maternal nutritional restriction or stress during foetal development on health during adult life (Greenwood and Bell 2003a,b; Bell et al. 2005).
Table 1 Consequences of growth in utero for growth and liveweight characteristics of beef cattle to 30 months of age. Prenatal growth/birth weight Low (n = 120)
High (n = 120)
Significance of difference (P)
Birth weight (kg)