loin clepih measuremeni was taken. by an RELATIONSHIPS BETWEEN CARCASS WEIGHTS, BACKFAT AND LOIN MUSCLE DEPTH IN CULL SOWS

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1 RELATIONSHIPS BETWEEN CARCASS WEIGHTS, BACKFAT AND LOIN MUSCLE DEPTH IN CULL SOWS i The carcass weight distribution ofthe cull sow population was evaluated from sows slaughtered in Ontario in Carcass weight, backfat depth and loin muscle depth were evaluated for 797 additional sows, randomly selected at a commercial abattoir. Approximately 85% of sows were between 100 and 200 kg with 4.5% less than 100 kg and 10.5% more than 200 kg carcass weight. The frequency distribution showed backfat depth was most frequently between 15 and 19.9 mm (26.73%) and 20 and 24.9 mm (29.99%). Sow carcasses are extremely diverse, varying 3- to g-fold in backfat depth and 2- to 3-fold in loin muscle depth within any 25-kg weight class. Key words: Sows, carcass composition, backfat IRapports entre le poids de la carcasse, l'6paisseur du lard dorsal et la profondeur du muscle de la longe chez des truies de r6forme.l Titre abr6g6: Caractbres de la carcasse de truies de r6forme. La r6partition des poids de la carcasse du cheptel de truies de r6forme a 6t6 6valu6e chez truies abattues en Ontario en Le poids de la carcasse, l'6paisseur du lard dorsal et la profondeur du muscle de la longe ont 6t6 6valu6s chez 797 truies suppl6mentaires, chbisies au hasard dans un abattoir commercial. Environ 85% des truies se situent entre 100 et 200 kg de poids, les limites 6tant de 4,5% moins que 100 kget del0,5% plusque200 kg. Ladistributiondefr6quencemontrequel'6paisseur du lard dorsal se situe le plus souvent entre 15 et 19,9 mm (26,73%) et 20 et 24,9 mm (29,99%). Les carcasses des truies sont trds diversifi6es, variant de 3 ir 9 fbis pour ce qui est de l'6paisseur du lard dorsal et de 2 d 3 fois pour ce qui est de la profondeur du muscle de la longe dans n'importe quelle classe de poids de 25 kg. Mots cl6s: Truies, composition de la carcasse, lard dorsal The carcass characteristics of cull sows have Knowledge of the distribution and relationships not been investigated in Canada although of carcass characteristics is important in sows are slaughtered every year. guiding future research on a grading system This only represents 2.8% of the total number for sows and for future assessments of of pigs slaughtered; however, because of the change over time in the characteristics of the higher average carcass weight, the meat from population. sows accounts for about 5.6% of the total pork The objective of this research was to market. A search of the literature revealed determine the distribution and relationships that the only information available on carcass between carcass weight and fat and loin depth composition of sows was as a result of nutri- in slaughter sows. tional or reproductive experiments (e.g. Data on carcass weights of sows Kirkwood et al. 1988; and Yang et al. 1989); slaushtered in Ontario from January 1988 to in which the method of data collection was 3l dec were obtained from th-e Ontario generally unsuitable for calculations of lean pork producers' Marketing Board to deteryield, and the range in carcass weight was minethenormaldistributionof weightinthe small. Also, these types of experiments give slaughter sow population. no information on the characteristics of the Dita were also iollected at a meat packing ;:::xlo3t.',i*:'""f ;i ;ll ;"J:,n.?r:fi ij?*t9"*'y,y:,il,'fi:::: i""t":;"3j1 carcass weight over the normal market range. accordine to commercial practice. One fat and loin clepih measuremeni was taken. by an Can. J. Anim. Sci. 70: (Dec. 1990) Agriculture Canada grader, on the split warm I l4l

2 1142 CANADIAN JOURNAL OF ANIMAL SCIENCE carcass within I h postmortem using an electronic probe (Destron International, Markham, ON, Model PG-100) between the 3rdl4th last ribs 7.0 cm from the midline. Some difficulties were found when probing sow carcasses, including: the speed at which carcasses passed the probing station, pathological conditions and inadequate length ofthe probe shaft for very thick carcasses. Probing errors occurred for 14% of the total attemdts because the probe shaft was too short to penetrate into the body cavity, therefore very fat sows are underrepresented in this sample. Muscle depth measurements of 3l of the 797 sows were eliminated due to equipment error. The frequency distribution and measures of dispersion were determined for hot carcass weight, fat depth and loin depth (Statistical Analysis Sysrem Institute, Inc. (SAS) 1985a). Distribution of fat and loin deoth was also determined within weight classes. arbitrarily set at 25-kg increments. Regression analysis (SAS 1985b) was used to evaluate the relationships between carcass weight, fat depth and loin depth. To our knowledge this is the first published report of carcass characteristics of the commercial culled sow population. The mean (tsn; carcass weight of sows Table 1. Thefrequencydistribution(%),mean Weight class (kg) t t No. of sows Mean SD Onrtarioz frequency (%) t , Frequency (%) t {r 3t.17 slaughtered in Ontario during 1988 is shown in Table 1. These data indicate that the majority of the sows slaughtered in Ontario, approximately 85%, were between 100 and 200 kg carcass weight, and 50% of the sows fell within a weight range of 50 kg, from 125 to 175 kg. The sample frequency (%) within weight class and mean + SD for fat depth and muscle depth are also presented in Table 1. The similarity of the mean carcass weights and distribution of the sows slaughtered in Ontario in 1988 and the sample of 797 sow carcasses reported here indicates that our sample was representative of the larger population, with the exception of the sows over 225 kg carcass weight. When weight classes I and 8 were eliminated and frequency distribution of the other weight classes was recalculated, the distributions became even more similar with a difference of less than l% from the frequency of the larger population (data not shown). The shaft of the grading probe was not long enough to probe all the sows in weight classes 7 and 8; therefore, these weight classes are biased due to the fact that sows with very thick fat or lean are u nderreoresented. Mean fat depth increased consistently with increasing carcass weight (Table l) except for f SDandrangeof fatthicknessof sowsofdifferentcarcassweight classes Fat thickness (mm) Mean f SD (mm) tt 6.t l Frequency (%) 5.)l 18. l Muscle depth Mean t SD (mm) t r 'All sows marketed in Ontario in 1988 via the Ontario Pork Producers Marketing Board rweight (kg). 'Depth (mm).

3 AZIZ ET AL. CARCASS CHARACTERISTICS OF CULL SOWS r 143 between 225 and kg, probably due to inability to probe the fattest sows. The range in fat depth within weight class varied 3- to 9-fold from the mean, showing that there were both extremely lean and extremely fat sows in every weight class. Fat depths as low as 6 mm and as high as 66 mm were recorded. Muscle depth was less variable than fat depth, varying 2- to 3-fold within weight classes, and if lowest ( < 100 kg) and highest ( > 250 kg) classes are excluded, the range of the means was only l0 mm. These data show that, both within and across carcass weight classes, the slaughter sow population is extremely variable in fat and muscle deoth and thus probably also extremely variable in lean yield. The fat class distribution both across and within each weight class are shown in Fig l. The percentage ofsows in each fat class, independent of weight, were: class 1 (< 9.9 mm) 0.75%, class 2 ( mm) 12.l'7%, class 3 ( mm) 26.13%, class 4 ( mm) 29.99%, class 5 ( mm) 14.18%, class 6 ( mm) g 140 o eflo o p roo BO % and class 7 (> 40.0 mm) only 3.01%. These data show that 40% of sows had 19 mm or less of backfat and thus could be described as very lean, even by market hog standards. The frequency distribution of sows by fat class within weight classes (Fig. l) indicated that the frequency distribution for fat thickness changed although mean fat thickness increased only slightly with increasing weight (Table 1). For example, fat class 2 ( mm) accounted for a small proportion of sows, 25, 18 and 6% inweight classes 2, 3 and 4, respectively, while fat classes 3 ( mm) and 4 ( mm) accounted for the majority of sows in weight classes 2,3 and 4. The proportion of sows in these weight classes with24.9 mm or less of backfat were 85, '19 and 70%, respectively. The frequency distribution of loin muscle depth both across and within each weight class was also calculated. The percentage of sows in each loin depth class, independent ofweight were: class 1 (< 29.9 mm) 1.6%, class2 fat classes (mm) N m E ffi n M I > 4o.o < weight class Fig. 1. The frequency distribution of fat depth within weight class of 797 sows

4 1 144 CANADIAN JOURNAL OF ANIMAL SCIENCE ( mm) 6.6%, class 3 ( mm) 20.6%, class 4 ( mm) 31.2%, class 5 ( mm) 29.1%, class 6 ( mm) 3.5%, and class 7 (= 80.0 mm) 1.3%. The distribution of loin muscle depth within weight classes varied widely although mean muscle depth (Table 1) did not. For example, muscle depth classes 3, 4 and 5 accounted for 32.4, 30.9 and 20.1% of sows in weight class 2; 25.0, 34.6 and28.4 in weight class 3 and 13.1, 41.6 and 30.1 in weight class 4, respectively. The relationships between carcass weight and fat and loin depth were determined by regression. Weight classes 7 and 8 were excluded from the regressions due to the small number of observations and Dotential for bias in both groups due to the problem with the length of the probe shaft. Loin muscle depth increased by mm as the carcass weight increased by 1 kg (tt : A.126x, r :0.3571, SE : 0.012). There was a linear increase of fat depth by mm as the carcass weight increased by I kg ()' : x, r : , SE : 0.008). Plots of fat depth and muscle depth against weight showed no apparent plateau, indicating that even at 200 kg carcass weight these sows were still depositing both muscle and fat, and in this sense were still growing. The similarity in the regression coefficients for fat depth (0.124) and loin depth (0.126) indicates that both fat and muscle depth increased at similar rates, whereas in market pigs, backfat depth increases at higher rates ( (McKay and Garnett 1988)). Jones et al. ( 1980) also found that total side fat of market pigs increased at a significantly higher rate than total side muscle. This difference between sows and market pigs is probably due to the loss of fat by sows during cycles of pregnancy and lactation (Close and Cole 1984; Whittemore and Yang 1989) but important interactions could also occur with environmental conditions (e.g. ambient temperature) and nutrient intake (Kemp et al. r987). This evaluation ofcarcass weights, fat and loin depth in culled sows showed that the population was extremely variable in all parameters. This variation of fat depth (3- to 9-fold) and loin depth (2- to 3-fold) within weight classes means that a system of pricing sows on a carcass weight basis only, will probably result in the prices of a large number of sows not being representative of their true value as represented by yield of lean meat. Therefore, further research involving dissection of a large number of sows and subsequent development of regression equations to predict body composition of both live sows and carcasses would be useful both for developing a carcass grading system based upon lean yield and for estimating body composition of sows in nutrition and reproductive researcn. ACKNOWLEDGMENTS This work made possible by a grant from the Ontario Pork Producers' Marketing Board. The authors wish to thank Agriculture Canada fbr technical assistance and Quality Meat Packers, Toronto for their assistance and indulgence. Close, W. H. and Cole, D. J. A Principles and strategies involved in the nutrition of the sow. 35th Annual Meeting of the European Association of Animal Production, The Hague, The Netherlands. Jones, S, D. M., Richmond, R, J., Price, M. A. and Berg, R. T Effects of breed and sex on the patterns of fat deposition and distribution in swine. Can. J. Anim. Sci. 60: Kemp, B., Verstegen, M. W. A., Verhagen, J. M. F. and Yan Der Hel, W The effect of environmental temperature and feeding level on energy and protein retention of individually housed pregnant sows. Anim. Prod. 44: 2' Kirkwood, R. N., Mitaru, A, D., Gooneratne, R. B. and Thacker, P. A The influence of dietary energy intake during successive lactations on sow prolificacy. Can. J. Anim. Sci. 68: McKay, R. M. and Garnett, I Growth and fat deposition curves in swine. Can. J. Anim. Sci. 68: 57-6'7. Statistical Analysis System Institute, Inc. 1985a. SAS user's guide: Basics. Version 5 edition. SAS, Cary, NC. ll81 pp. Statistical Analysis System Institute, Inc. 1985b. SAS user's guide: Statistics. Version 5 edition. SAS, Cary, NC. 655 pp.

5 AZIZET AL. - CARCASS CHARACTERTSTICS OF CULL SOWS I 145 Whittemore, C. T. and Yang, H Physical and chemical composition of the body of breeding sows with differing body subcutaneous fat depth at parturition, differing nutrition during lactation and differing litter size. Anim. Prod. 48: Yang, H., Eastham, P. R., Phillips, P. and Whittemore, C. T Reproductive performance, body weight and body condition of breeding sows with differing body fatness at parturition, differing nutrition during lactation, and differing litter size. Anim. Prod. 48: N. N. AZIZ1, W. A. RAEI, J. W. ALLAN2, and R. o. BALLr,3 tdepartment of Animal and Pouhry Science, Universiry of Guelph, Guelph, Ontario, Canada NIG 2Wl, and 2Agriculture Canada, Food Production & Inspection Branch, 4900 Yonge Street, Suite 1220, Toronto, Ontario Canada M2N 6G6. Received 20 Oct. 1989, accepted I0 Aug rsend reprint requests to R. O. Ball.

6 This article has been cited by: 1. Caitlyn E. Abell, Kenneth J. Stalder, Haven B. Hendricks, Robert F. Fitzgerald Cull sow knife-separable lean content evaluation at harvest and lean mass content prediction equation development. Meat Science 91:3, [Crossref]