Performance of pigs fed diets containing turnip weed seed (Rapistrum rugosum).

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 16 PERFORMANCE OF PIGS FED DIETS CONTAINING TURNIP WEED SEED (RAPISTRUM RUGOSUM) A. TAKKEN*, I. GRIFFITHS ** and M.H. MAGEE* SUMMARY The substitution of turnip weed seed (TW) for wheat in pig diets resulted in a linear decline in average daily gain (ADG), poorer food conversion (FCR). and a decrease in voluntary daily food intake (DFI) above 18% TW. For each 1% inclusion of TW, ADG fell by 1.3% and FCR worsened by 1.0%. There were no differences in carcase quality between treatments and a taste panel asessment of meat flavour did not detect any unusual meat taint attributable to the TW. (Keywords : meat taint, turnip weed seed, growth performance, pigs) INTRODUCTION Turnip weed (TW) is a widespread contaminant of winter cereals. This annual herb seeds prolifically and grows in any disturbed ground. Feed grain samples containing >20% TW seed have been seen at this laboratory. TW, like many of its plant relatives (Brassicas) is known to cause the tainting of meat and milk (McBarron 1977) when grazed. The seeds of many of these plants contain extremely irritant mustard oils and other toxic compounds which are known to affect palatability of pig diets. TW seed has a strong odour and at the levels of contamination in grain observed in the field and laboratory, has the potential to affect pig performance and may cause meat taint. An investigation with pigs of these potential problems is reported here. MATERIALS AND METHODS (i) Diets Commercial wheat gradings containing TW were processed through a laboratory screening machine to produce a stock of pure TW. The proximate, gross energy and selected amino acid analyses of the individual ingredients were determined according to the procedures described by Connor et al. (1971) and are given in Table 1. Eight diets were prepared using roller milled ingredients by substitution of TW seed for wheat in a basal diet which contained (g/kg); 770 wheat, 180 soyabean meal, 30 Ca2HP04, 5 NaCl, 5 vitamin and trace mineral premix and 10 vegetable oil. TW seed was substituted in increments of 30 g/kg from 0 to 210 g/kg. Levels of dietary crude protein (CP), crude fibre (CF), total lysine and predicted digestible energy (DE) are given in Table 2. Dietary DE values were calculated using the prediction equation (No. 25) of Batterham et al. [1980]. (ii) Animals Ten-week old pigs, 16 male and 16 female, were assigned at random within sex groups to the eight dietary treatments according to a randomised block design. The mean live weight 2 standard deviation of the male and female pigs at the start and end of the experiment were respectively, 22.0 2 1.18 kg; 21.7 2 1.34 kg and 84.1 f 2.83 kg; 82.6 t 3.09 kg. (iii) Management Pigs were individually housed and fed ad libitum; water was available at all times. Feed spillages were collected daily and the oven dried weight used to calculate actual feed intake. Pigs were weighed weekly and removed from the experiment at the first weighing of 82 kg or more. * Dept. of Primary Indus tries, An imal Research Ins t i tute, Ye erongpilly, Q. 4105 ** CSIRO, Div. of Food ReIS. , Meat Research Laborato rY , Cannon Hill, Q. 4170 375 Proc. Aust. Soc. Anim. Prod. Vol. 16 (iv) Carcase appraisa l Carcases were appraised as described by Williams and Daniels (1973) with the modification that the left ham was removed by a transverse saw cut immediately anterior to the symphysis pubis (Joblin, 1966). (v) Taint appraisal A section of loin meat from each c&case was dissected into lean meat, fat and trim. Lean plus 10% fat was stored frozen in sealed C, polyethylene bags until required. After partial thawing for 16 hrs at 5' the fat was finely cubed, mixed with approximately twice the quantity of lean and twice minced through 4 mm holes. The remainder of cubed lean was then added and the mixture again minced through 4 mm holes. 500 g of mince plus 500 g of water was brought to the boil in a stainless steel saucepan and gently simmered for 20 min. Approximately 25 g of sample was placed in a 50 ml glass beaker covered C with foil and allowed to stabilise in a warming oven at 75' for 15 min. A panel of 22 experienced meat flavour and taste assessors was formed and the meat samples appraised over a number of tasting sessions. At each session, each member was presented with four coded samples which were scored for meat and other aromas, meat and other flavours and overall acceptability. Aroma and flavour intensities were rated on a 9 point scale (O-none, e-slight, 4-moderate, 6-strong and 8-very strong) and overall acceptability rated using a g-point hedonic scale (O-very poor to 8-very good). All 8 treatments were assessed from either male or female pigs each day. Taste paneLmembers were encouraged to provide descriptive comments on the nature of any unusual aromas or flavours; additional or alternative terms were permitted. (vi) Statistical analysi s Data was subjected .to ananalysis of variance isolating effects due to diet, sex and associated,,interactions. Regression analysis was used to examine the effect of TW:in the diet on pig performance. Table 1 Chemical composition of the maindietary ingredients (as fed basis) Table 2 Chemical analysis of the experimental diets RESULTS Apart from sporadic cases of diarrhoea, of less than 24 h duration in the early experimental period, all pigs maintained good health at all times. The interaction between the main effects of sex and diet was not significant. Male pigs ate less total food (166.8 vs 176.3 kg) but more per day (2.41 vs 2.33 kg), used food more efficiently (2.75 vs 2.92) and grew faster (884 vs 807 g/d) than females (PcO.05). Dressing percentage was lower (PCO.05) in males than females (73.7 vs 76.1%). 376 Proc. Aust. Soc. Anim. Prod. Vol. 16 Table 3 Daily gain (ADG), feed conversion (FCR) and daily feed intake (DFI) of pigs and meat appraisal for aroma (A), flavour (F) and overall acceptability (OA), with the standard error of the means (SEM) Average daily gain (ADG), feed conversion ratio (FCR) and voluntary daily feed intake (DFI) of the pigs are given in Table 3 and the relationship of these responses to dietary level of TW is presented in Table 4. ADG and FCR deteriorated linearly (PCO.01) with increasing TW in the diet. DFI was not significantly affected by TW except for a marked depression at the highest level. Flavour, aroma and overall acceptability of the meat was unaffected by TW (Table 3) nor did TW affect carcase measurements. Table 4 Relationships between performance (Y) and dietary TW seed (X) DISCUSSION Investigation of the effects of TW on diet digestibility was abandoned when pigs refused to eat their ration, after water was added, even at the 3% TW level. This was in marked contrast to the dry fed diets where voluntary food intake was not significantly reduced until the TW level exceeded 18%. It was noted that moistening the feed increased the odour released by the TW. The inverse relationship between percentage crude fibre and digestibility is well known and has led to the formulation of many equations for predicting DE in diets or ingredients (Batterham et al. 1980, Morgan and Whittemore, 1982). That (No. 25) of Batterham et al. (1980) predicts that dietary DE will fall from 13.6 to 11.2 MJ/kg as the TW level increased from 0 to 21%. It is well documented (Owen and Ridgman 1968) that under ad libitum feeding regimens pigs will compensate for reduced dietary DE content by increasing voluntary DFI. This effect was not observed in this experiment. In fact DFI was suppressed at the highest level of TW inclusion. The observed excellent growth rate obtained from the control diet and the fact that the lysine to energy ratio improved with the inclusion of TW indicates that some other factors were responsible for the reduced growth rate and the lack of increased voluntary DFI observed. Palatability was probably responsible for the DFI effect whilst the reduced ADG and poorer FCR were the result of the dietary DE dilution by fibre. It has been clearly established that fibre depresses the digestibility of other dietary Proc. Aust. Soc. Anim. Prod. Vol. 16 components such as protein (Cole, 1974), energy (Henry, 1976) and that fibre utilisation in the pig is poor, due to a lack of fibre-digesting enzymes (Cranwell, 1968). The absence of significant taint was surprising. Taints are generally chemicals or ,the absorption of seconda expression of taint in ruminants and n differences in the digestive processes the absorbed digesta. in the meat caused by t ry metaboli ot in pigs and pathwa 9 especial he direct tes from t is probabl ys of furt ly at high TW intake uptake of foreign .he digesta. The y a function of the .her utilisation o f It is concluded that TW appears unlikely to cause overt toxicity or mea t taint but its unpalatability gives some reason for concern, especially if fed wet. At high levels of inclusion special attention should be paid to the diluent and depressant effect of the crude fibre on both energy and other nutrients. ACKNOWLEDGEMENTS This investigation was generously supported by the Australian Pig industry Research Committee. We thank Dr. A. Neil1 and the staff of Biochemistry Branch, DPI for analysis of feed ingredients, Mr. P.N. Jones, CSIRO Div. of Mathematics and Statistics and members of the CSIRO., Div. of Food Res., Cannon Hill, Taste panel for their assistance in the meat quality testing. The feed milling industry is thanked for providing raw materials. REFERENCES BATTERHAM, E.S., LEWIS, C.E., LOWE, R.F. and McMILLAN, C.J. (1980). Anim. Prod. 31: 259 . COLE, D.J.A. (1974). In 'Nutrition Conference for Feed Manufacturers: 7', p.81., editors H. Swan and D. Lewis. (Butterworths, London). CONNOR, J.K. , NEILL, A.R. and BURTON, H.W. (1971). Aust. J. Exp. Agric. Anim. Husb. 11: 387. CRANWELL, P.D. (1968). Nutr. Abstr. Rev. 38: 721. HENRY, Y. (1976). In 'First International Symposium, Feed Composition Animal Nutrient Requirements, and Computerisation of Diets'. p.270. editors P. Fonnesbeck, L.E. Harris and L.C. Kearl. (Utah State University: Logan, Utah). JOBLIN, A.D.H. (1966). N.Z. J. Agric. Res. s 241. McBARRON, E.J. (1977). In 'Medical and Veterinary Aspects of Plant Poisons in New South Wales'. 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