Low glucosinolate full-fat rapeseed meal in the diets of early-weaned piglets

Diets for young pigs

In the United Kingdom, the majority of pigs are weaned at 3 to 4 weeks of age. Prior to weaning the main source of nutrients is milk produced by the sow. After weaning, suitable complete diets need to be given that are compatible with the physiological state of the digestive system and supply adequate nutrient inputs to achieve maximal growth with minimum digestive upset. The weaning process, however, imposes considerable stress on the piglet which frequently results in a retardation of growth, often accompanied by problems associated with diarrhoea.

The challenge to the commercial nutritionist and the pig producer is to achieve sufficiently high nutrient intakes to reach the maximum growth potential. Improved understanding of the digestive physiology of the weaned pig and better estimations of the nutrient requirements of genetically improved stock has led to the development of appropriate diet specifications. There is a perpetual need to reconsider the most suitable food ingredients to use in diet formulations to meet these nutrient specifications, due to economic circumstances. The food ingredients need to be highly digestible, extremely palatable and to contain no anti-nutritive factor or antagonist to the digestive process. The food form and method of feeding can greatly influence food intake post weaning. The piglet weaning weight to age relationship can also affect the subsequent food intake, growth rate and incidence of problems associated with diarrhoea.

There are continual changes and developments within the animal food and pig production industries that affect nutrition of the young pig. These include genetic selection for prolificacy, development of outdoor pig breeding systems, ‘green issues’ including welfare and use of food additives, use of enzymes and probiotics and improvements in food production technology. In the development of diets for young pigs all these aspects need to be considered in achieving an optimal solution in terms of nutrition, management and economics.

The effect of protein source on the diets selected by pigs given a choice between a low and high protein food

To test the effect of the protein source on the diet selection of growing pigs, four foods of high protein concentration were made. Each food was based on a different protein meal: fish, soya bean, and two types of rape seed (with low and high glucosinolate contents), and was offered to growing pigs together with a food of low protein concentration (L), as a choice. Pigs given a choice between the fish or the soya bean meal-based food and L, selected a diet that met their protein requirements, as judged by their growth rates and food efficiency: the protein content of the selected diet declined systematically with pig weight. Pigs given a choice between the rape seed meal-based foods and L selected diets with a high proportion of L and, consequently, failed to meet their protein requirements. Given that the preference for L was more marked when the animals were given access to the rape seed meal higher in glucosinolates, it is suggested that their diet selection on these foodpairs was a tradeoff between minimising glucosinolate intake, which has potentially goitrogenic properties, and achieving a protein intake sufficient for maximum performance. This suggestion is supported by the fact that the fish meal-based food was preferred over the ones containing rape seed meal, and that the rape seed meal lower in glucosinolate content was preferred over the other when pigs were given a choice between them.

Feeding of rapeseed presscake meal to pigs: effects on thyroid morphology and function and on thyroid hormone blood levels, on liver and on growth performance

Effects of feeding soybean meal (SBM) or a mixture of SBM and 5%, 10% and 15% of either 0- and 00-rapeseed presscake meal (RPM) on thyroid, liver and growth performance were studied in castrated boars. Goitrin (G) intake was closely correlated with total glucosinolate intake and blood thiocyanate concentration. In pigs fed 10% and 15% 0-RPM refused feed was enhanced and daily gain decreased. Liver weight and DNA/total liver increased with increasing G intake. Thyroid weights increased up to a G intake of 4.6 mmol/d and then decreased with higher G intake. DNA content/g dry matter (DM) increased continuously and total thyroidal DNA content up to a G intake of 4.6 mmol/l, indicating hyperplasia. Epithelial thickness increased up to a G intake of 13.3 mmol/d, whereas follicular area only up to an intake of 4.6 mmol G/d and then decreased, mirrored by a decrease of DM content. Thyroidal thyroxine (T4) and triiodothyronine (T3) content decreased with increasing G intake. Blood serum levels of T4 decreased with increasing G intake, whereas T3 levels only tended to decrease. Therefore, measured parameters differently reacted to different G intake. In groups fed high amounts of G, hyperplasia was not sufficient to maintain physiological circulating T4 levels, but enhanced thyroidal secretion T3 and/or extrathyreoidal T4 to T3 conversion obviously allowed maintenance of near normal circulating T3 concentrations and barely reduced growth rate despite marked hypothyroidism.

Selection of a diet by growing pigs given choices between foods differing in contents of protein and rapeseed meal

The objective of the experiment was to test whether the rules that appear to underlie diet selection by pigs given choices between two foods of different crude protein (CP) content, persist when a rapeseed meal with possible goitrogenic effects is included in one or both foods. Forty-four pigs were given access to one food, or to two foods as a choice, from 12-30 kg liveweight. The foods were the combinations of two levels of CP (140 and 300 g CP/kg food) and two levels of inclusion (0 and 180 g/kg food) of a rapeseed meal, which resulted in foods L, H, LR, HR; in addition the equal parts mixture of foods L and H was also made (food M). The treatments were: access to a pair of foods as a choice, pairs LH, LR, H, LHR and LRHR (n = 6 per treatment) or access to a single food L, LR, M, H and HR (n = 4 per treatment). The inclusion of the rapeseed meal did not significantly affect the rates of food intake and liveweight gain of the pigs given access to one food. Pigs given a choice between a rapeseed-based food and another one (pairs LRH and LHR), showed a significant preference for the food without it. The rejection of the foods with rapeseed meal was such that it overpowered the physiological need of the pig to select a diet that would meet its CP requirement. When the two foods differed only in CP content (pairs LH and LRHR) pigs were able to select a diet whose composition changed systematically as they grew, and supported rapid growth. The diet selection of the choice-fed pigs is consistent with the idea that pigs, given a choice between a potentially harmful food and a non-harmful one, will favour the latter irrespective of its nutritional properties, only if it is assumed that the inclusion of rapeseed meal had a detrimental effect on the single fed pigs, which could not be seen in their performance as measured by the rates of food intake and liveweight gain.