The nature of the starch source (rapidly digestible, slowly digestible and resistant starch) may influence growth traits, as well as carcass and meat fatness, and such effect would depend on the rate glucose is released from its digestion, i.e., the changes in blood glucose concentration (glycemic index, GI). The GI is also related with the feeding pattern, since high postprandial glucose level induces long-lasting effects on satiety. The objective of this work was to evaluate whether the glycemic index (GI) of the starch source may affect growth and fattening of growing-finishing pigs. Thus, four sources of starch (barley, broken rice, maize and peas) differing in their digestion rates were characterised in vitro, and their GIs were estimated. Then four experimental diets were formulated to include 420 g starch/kg, provided by barley (B), barley/broken rice (R), barley/maize (M) or barley/peas (P) for growing pigs and their productive performances, diet digestibility and quality traits were tested.
The in vitro characterization of feeds showed that the rapidly digestible starch fraction was highest for R (P<0.001), whereas the slowly digestible fraction was higher for B and M. Then the resistant starch fraction was higher for P. The rate of glucose release was fastest with R (P<0.001), and estimations of glycemic index were highest for R and lowest for P (P<0.001). For the in vivo trial, a total of 72 crossbred gilts, with 63.0±4.55 kg body weight were used. Statistical trends were observed for ADG and FCR; gilts fed diet P grew faster (P<0.05) and had a lower FCR (P<0.05) than those fed diet R. The apparent organic matter digestibility for diets R and P was lower than for diet B (P<0.001) but higher than for diet M (P<0.01). Similarly, the apparent crude protein digestibility was higher with diet R than with diet M (P<0.01). Gilts consumed from 32% to 40% of available feed within the first 2 h after offering, then the rate dropped from 2 to 4 h (P<0.05) and was virtually nil from 10 to 12 h for all diets. There was not clear influence of diet on carcass yield or carcass length and meat characteristics. The intramuscular fat from pigs fed B showed higher (P<0.001) total saturated fatty acids and lower (P<0.001) total monounsaturated fatty acid contents than that from pigs fed M.
It is concluded that the availability of starch from feeds in the digestive tract offers a potential nutritional tool to reduce carcass fat accretion with slowly available starch sources, whereas the opposite should occur with readily digestible starch sources such as rice. However, the effects observed on marbling and on fat composition suggest that changing the starch source is not an effective strategy to qualitatively modify pork fat and meat.
Doti, S., Suárez-Belloch, J., Latorre, M.A., Guada, J.A. and Fondevila, M. 2014. Effect of dietary starch source on growth performances, digestibility and quality traits of growing pigs. Livestock Science 164; 119–127. http://dx.doi.org/10.1016/j.livsci.2014.03.016