2. Lean and fat development in piglets

Abstract

Piglets are immature at birth, which renders them highly sensitive to environmental conditions during the neonatal period. Lean and fat tissues are important components for survival and later growth capabilities. This chapter focuses on the development of skeletal muscle and adipose tissue during intra-uterine life, suckling and post-weaning. Available data show that the profile of myosin heavy chain isoforms and the glycogen content are good descriptors of skeletal muscle maturity around birth. Expression levels of key genes such as DLK1 and IGF2, regulating the transition from proliferation to differentiation of constitutive cell precursors, could also be assessed as indicators of the relative level of maturity in adipose tissue at this period. The provision of nutrients to foetuses affects the development of muscle and adipose tissues during gestation and alters their functionalities after birth. Spontaneous intra-uterine growth restriction markedly delays the genetically programmed development of lean and fat tissues and especially impairs the formation of myofibres, thereby reducing the adaptive abilities of small neonates to the extra-uterine environment. Maternal energy or protein overfeeding have no beneficial effects on muscle development in foetal pigs, but nutritional avenues using supplementary arginine or vitamin D in sow diets at specific periods of gestation may be favourable for foetal myogenesis. The best strategies to increase body fat content before birth and enhance lipolytic and oxidation capacities of piglets soon after birth remain to be developed. During the suckling period, myofibre composition and size undergo marked changes. Adipose tissue growth is also accelerated and this is exacerbated in small littermates with detrimental effects on their physiology later in life. Supplementing the diet of suckling or post-weaned piglets with branched-chain amino acids could improve muscle maturation and affect adipose tissue metabolism. With the multiplicity of factors acting on the development of muscle and fat tissues in piglets, identifying optimal feeding strategies remains difficult.

Protein turnover in pigs: A review of interacting factors

“…Myofibers are the functional contractile unit of skeletal muscle, accounting for 75−90% of this tissue (Joo et al, 2013). The process of hyperplasia occurs mainly during the fetal period, and the total number of myofibers is considered to be stablished at around 90 days of gestation (Gondret et al, 2020), remaining practically constant during the postnatal period. However, myofiber size appears to remain almost unaltered during the prenatal period, with hypertrophy occurring mainly after birth (Lefaucheur, 2010).…”

“…During the embryonic and fetal period, the predominant MyHC isoform is slow-twitch type I, although by late gestation the adult fast-twitch types IIa and IIx isoforms appear. It is at birth that a large part of the type I MyHC isoforms mature to fast-twitch isoforms, and type IIb MyHC isoform also emerge (Gondret et al, 2020). The intensity with which the proportion of slow-twitch myofibers changes to fast-twitch myofibers decreases with pig maturation (Fazarinc et al, 2017).…”

“…The significant decrease in the number of satellite cells with age (ii) (Neal et al, 2012). Satellite cells proliferate and differentiate intensively during the postnatal period, contributing to myofiber hypertrophy by fusing with them (Gondret et al, 2020). Finally, modification of the MyHC myofiber profile (iii) (Brocks et al, 2000; Saxton & Sabatini, 2017).…”

1. The neonatal pig: developmental influences on vitality

“…This fat is important for thermoinsulation and is also a readily available source of energy. Energy metabolism of newborn piglets is covered in detail in Chapter 2 (Gondret et al, 2020). Variations in carcass composition among piglets at birth are smaller than at 10 days of Glycogen is a most important energy store in newborn piglets.…”

“…Colostrum also provides approximately 75% of the energy required for heat production at 24 °C (Herpin et al, 1994). Yet, the amount of colostrum ingested may be insufficient to ensure thermoregulation, largely because of a poor utilization capacity by newborn piglets (see Chapter 2, Gondret et al, 2020), and heat lamps must therefore be used. Indeed, in contrast to older pigs, neonatal piglets do not increase their colostrum intake in response to cold temperatures but in fact decrease it, which further exacerbates the problem (Le Dividich and Noblet, 1981).…”