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Review article
A case for size and shape scaling for understanding nutrient
use in breeding sows and growing pigs
a ,
*
bC.T. Whittemore
, C.P. Schofield
a
The University of Edinburgh, Institute of Ecology and Resource Management, West Mains Road, Edinburgh EH9 3JG, UK
b
BBSRC Silsoe Research Institute, Wrest Park, Silsoe, Bedford MK45 4HS, UK
Received 22 December 1998; received in revised form 22 June 1999; accepted 20 July 1999
Abstract
New Visual Image Analysis technologies now allow the hitherto unattainable measurement of animal size and shape. Knowledge of size and shape (and volume) in addition to weight gives new dimensions to pig description. Sow body condition, and consequent nutrient requirement, can be directly and objectively determined for the first time since weight was questioned as an adequate datum upon which to base sow feeding requirements. Relationships could now be drawn for a more direct determination of fitness for slaughter, and of nutrient requirements; in the latter case evidently for maintenance but, on reflection, also for growth. So familiar has the scale of weight become that it is ill appreciated that weight is often used not only for its own sake but rather as an indirect estimation of size and shape. This paper examines the value of the estimation of size and shape for animal description in relation to nutrient use; if not to replace weight entirely, then at least to augment it. 2000 Elsevier Science B.V. All rights reserved.
Keywords: Growth; Nutrition; Size; Shape
1. Introduction of nutritional requirement were as concerned with
linear and volume measurements as with mass. The present presumption is that weight is the Brody (1945) expressed basal metabolism and the appropriate base for description and analysis of nutritional needs for maintenance first in terms of animal growth and for the determination of nutrition- linear size, surface area and volume: ‘‘In equation al adequacy, but not for the best of reasons: ease of form, one may say that surface, or heat loss, or heat accurate quantification. Size and shape was not production, or oxygen consumption, Y, is
propor-2
dismissed by Hammond (1932), or his disciples tional to the square of the linear size, L: Y~L ; or to
(Hammond, 1955), as a meaningful base for the the 2 / 3 power of volume [in the knowledge that description of growth and development. The volume varies with the cube of linear size], or to the originators of growth analysis and the determination 2 / 3 power of weight, W [if the specific gravity is
2 / 3
constant], as indicated by the equation Y5aW .’’ Subsequently, Brody makes much of the relationship *Corresponding author. Tel.: 144-131-535-4050; fax: 1
44-between surface area and liveweight from the stand-131-667-2601.
E-mail address: [email protected] (C.T. Whittemore). point of establishing W as a useful and correlated
indicator for surface area; that is, surface area is loin and back cuts. In the case of the breeding sow, it perceived as the appropriate base. is size (for example, of uterine capacity, gut capaci-Recently, however, consideration of size, shape ty, egg diameter, mammary volume) and shape and surface area has fallen out of use for purposes of (fatness) that are the measurements of interest; growth description as exampled by the recent re- weight being irrelevant to breeding success.
views of Bastianelli and Sauvant (1997), and Em- In some cases, information on live body weight mans and Kyriazakis (1997). The rejection of animal can be positively deceptive. Nutrient requirement size and shape in favour of animal weight seems then purports to relate to protein and lipid gains, but gain to be consequent more upon the difficulty of mea- in mass is primarily a gain of water. Water:fat and surement of the former rather than the aptness of the water:lean ratios in the body are fickle, varying with latter. Indeed, if a realistic alternative to weight as age, sex and physiological circumstances. Post wean-the scale of measurement of animal growth were to ing (4-week old piglets), and during lactation (breed-be available, many reasons could (breed-be forwarded as to ing sows), pigs will lose fatty tissue at a substantially the inappropriateness of weight as the sole descriptor greater rate than they will lose weight (Whittemore of choice. Weight can take no account of body et al., 1981) due to the influx of water. Weight losses development, shape and proportion; all so essential are thus contra-indicated as measures of lipid catabo-to an understanding of growth, the assessment of lism. Shape, on the other hand, is highly sensitive to animal value, and the determination of appropriate loss of body lipid, and the change in shape of the feeding strategies for gestating breeding sows. young growing pig, or the lactating and gestating The use of linear measurement as an alternative sow, is a far superior indicator of its nutritional scale to weight is constrained by the former being status than changing weight. It is well accepted that more difficult to determine. Brody (1945) himself loss of body shape (rounded to flat) post-weaning is describes tedious and complex methodologies es- a better indicator of nutritional adequacy than weight timating the surface area of animal bodies. Linear change, and growth rate in young pigs is effectively measurement necessitates multiple assessments, at estimated through visual assessment of their shape least of length, breadth, height and circumference, all and condition. Judgement of shape (condition) by of which have indeterminate reference points. Vol- subjective visual assessment is the industry standard ume may be a route to surface area, although for determining the nutritional requirements of ges-conventional water displacement is difficult with a tating sows.
live animal, and entrapment of air presents problems even in eviscerated carcasses. Specific gravity has
long been a recognised methodology for determining 2. Maintenance
the body composition (content of lower density lipid
tissue) of pigs post-mortem (Adam and Smith, 1964). Despite the frequent use of the base of metabolic
b
As a basis for the determination of nutrient body weight (W ) for expressing animal function, requirement, there is no prima facie case for a scale the value for b remains a variable (ARC, 1981) solely of weight to the exclusion of consideration of (between 0.56 and 1, but with 0.66 and 0.75 being size. Provision of nutrients for lean tissue growth is most common usage), and the transformation there-presently focused on weight of required protein fore appears less than adequate. The maintenance gains, but these gains are achieved with the purpose function accounts for one third or more of the energy of increasing muscle cell size, and it is as legitimate usage of a growing pig, and nearly all of the energy to conceive of protein growth in terms of expanding usage of the gestating breeding sow. The exponent volume and linear size of limbs and organs (cubic appropriate for maintenance may even be argued to millimetres of gain per day), as in terms of weight be inversely related to weight (Breirem, 1939;
¨
(grams of gain per day). This proposition is further Verstegen, 1971; Thorbek, 1974; Gadeken et al., legitimised if there is a desire to grow meaty, large 1973); Whittemore (1976), postulating b51.242
appro-priate if fat-free body mass were to be used. It is (1997) state ‘‘Growth has sometimes been defined as germane that fatness increases with pig weight, the rate of change in body weight . . . .. but the causes changes in shape, body volume, and surface development of the animal, e.g. change in body area, and progressively reduces the specific gravity composition, or in the relative importance of the of the body. different parts of the body, also needs to be included
in the definition’’.
Weight does not have a direct relationship with
3. Body composition and carcass value body composition expressed as the content or
pro-portions of fat and lean; change in weight can be of Strong correlations between weight and fatness, either fat or lean tissue. The weight scale therefore and between weight and shape are conventionally benefits from an estimate of body composition such observed in growing pigs fed to appetite (Whitte- as may be achieved in the live animal through more et al. 1988; Marchant et al., 1999). However, ultra-sonic measurement of fat depth. But fat depth is these are correlations resulting from the simultaneous not always an accurate predictor of lean mass, response of both sets of characters to nutrient supply; especially if more than one genotype is involved a presumption of any causal relation being most (Wood et al., 1991). This position is improved, unsafe. It is well understood that pigs can be grown, however, by the addition of muscle depth, and it is through nutritional manipulation, to be fat or thin at muscle volume – as may be appraised by size and any given weight (ARC, 1981). Changes in shape shape – that will give best prediction of lean content and fatness may be coincident with but not con- and carcass value.
sequent upon changes in size and weight. For purposes of the determination and provision of
nutrient requirement for growing meat pigs, where 4. Sow condition score and the nutrition of
fatness and shape is seminal to quality, weight breeding sows
change is a less than satisfactory measure. The
determination of appropriate slaughter point, either Weight (absolute weight or weight change) has in terms of handling at the abattoir or of ultimate long been shown unsatisfactory for determining the yield of saleable cuts, may be as much about animal nutrient requirement of reproducing sows (Whitte-size as animal weight. more et al., 1980; Whittemore, 1998), and has been Whittemore (1983) pointed out that growth beneficially replaced by a visual scoring system models may achieve deductive simulation of the which appraises the adequacy of nutrient supply mass of lipid and protein accreted, and by empirical according to condition score (Whittemore, 1998); regression, an estimate of eye-muscle area and back- this being a more effective monitor for body lipid depth, but that no deductive or empirical algorithms content. The basis of judgement for appropriate are available for the estimation of where in the body feeding tactics and strategies is therefore more the lipid (or protein) may come to be deposited; and appropriately one of sow size and shape than of sow that there can be no effective modelling of body body weight. Nevertheless, whilst feeding to con-development, or of body shape. Nonetheless, at the dition score (rather than weight) is now the accepted point of slaughter, quality in the carcass is dependent industry standard, it suffers from the shortcoming of not only on weight but also upon size (length, the subjectivity of the eye of the person in charge of volume), shape (ham and loin proportions), and day-to-day feeding.
determina-tion of individual sow weight at each visit to the reference to photographic standards, and was there-electronic sow feeding station have been taken to a fore a visual, semi-objective assessment. The com-higher degree of sophistication through the medium ponents of that visual score are likely to include (a) of a quasi ad libitum electronic feed system that perceived flesh (fat) cover (roundness) over the permits determination of individual average daily rump, loin and back; (b) roundness of the ham; (c) gains for groups of gestating sows offered the depth of fully-fleshed ham extending down the leg; availability of both high and low nutrient-density and (d) general appearance. It is relevant to note, in feed (Perez-Munoz et al., 1998). The fundamental relation to video-imaging systems (Marchant et al., problem with sow weight as a determinant of 1999), that the view is from directly above the nutritional requirement is not the lack of equipment, animal and therefore of the plan area of the back of however, nor the lack of sophistication, but rather the pig. This plan view accommodates (a), but for (b) that weight itself is an unreliable measure of physio- and (c) an oblique view (such as from the human eye logical status and of nutrient need due to (a) the situated behind and above the animal) is required. notorious variability in estimates for the energy value Pigs may grow in size (length, height) and weight of positive and negative weight change, and (b) the independently of shape (volume, width, and fatness) irrelevancy to breeding performance of body weight and vice versa. Thus pigs may grow heavier and considered without reference to body size and shape bigger without simultaneously growing fatter, and (fatness). may or may not develop simultaneous better-de-As a subsidiary part of their study on the re- veloped (meatier) hams. The presumptive general, productive performance of breeding sows, Whitte- albeit unsafe, correlation between increasing weight more and Yang (1989) measured (in addition to live and increasing fatness in the case of the ad lib-fed weight) body height, length and width, ultrasonic pig growing from 60–120kg live weight is, of (US) P2 backfat thickness (fat1skin 65 mm from course, spurious for the breeding sow and the the mid-line at the last rib), and condition score weaned piglet where increases in size and weight (10-point scale). If the changes during the course of simultaneous with decreases in shape and fatness are the third pregnancy may be taken as indicative for unremarkable (Whittemore et al., 1980; Yang et al., overall herd management needs, then it can be 1989). Correlations between size / weight and shape / calculated from their results that between weaning fatness are poor. For animals approaching maturity, parity 2 and parturition parity 3 respective per- the position is further complicated by the presence in centage changes occurring in height, body barrel national breeding herds of both ‘small fat’ and ‘big length, width across hams, US P2 backfat depth, thin’ genotypes (Whittemore, 1994). For the de-condition score and live weight were 2.5, 4.1, 9.5, termination and provision of nutrient requirement 27, 28 and 20. From this it may be implied that sow over multiple parities, therefore, weight per se is height and length is not particularly helpful in contraindicated.
indicating the extent of the pregnancy gains that might be needed by the sows to replenish body tissue
losses occurring in the course of the previous 5. Measurement of size and shape
lactation (which were substantial in this experiment);
neces-sarily unclean environment of the sow yard. Some The most effective method for the last is the manufacturers, dismayed that problems of weighing construction of simulation models. A number of pigs at feeding stations have not been fully resolved effective models have been published for growing after many years of development, see visual imaging pigs (see review of Emmans and Kyriazakis (1997) systems as a more worthwhile development prospect in addition to those described by Whittemore and (Henderson, M., personal communication). Fawcett (1976), Whittemore (1983) and Whittemore Recent work at Silsoe (Marchant et al., 1999) has (1998)); but for breeding sows there has been little shown how image analysis of overhead visual im- published development beyond the propositions of ages of the plan of a standing pig can give de- Whittemore and Morgan (1990), and none of the terminations of change in plan surface area over time published models is suitable for present purposes which bear close resemblance to change in weight because their scales are weight and not shape and over time, and for which the correlation between the size. Given the technology of visual image analysis two regressions (visual image of plan on time; and the (hitherto unattainable) ability to measure weight on time) is high. Marchant et al. (1999) objectively animal size and shape, it would appear present equations W5a1bX, where W is weight reasonable to consider these latter as appropriate for
2
(kg), X is the plan (m ) view area of the pig, and investigation as scales for pig description in relation where the s.e. values are: 0.63 for (a); 3.5 for (b); to nutrient use.
and less than 0.5kg for the prediction. This may be taken as evidence for the efficacy of the visual
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