To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Data from pigs between 12 and 120 kg live weight were used to develop a relationship between the capacity for food bulk and live weight. High bulk foods, intended to limit growth, were offered for 21 days to pigs of 12, 36 (600 g sugar-beet pulp per kg (SBP60)) and 108 (800 g sugar-beet pulp per kg (SBP80)) kg live weight. Control pigs were given a low bulk food C at all weights. After 21 days the pigs were slaughtered and measurements made on the gastro-intestinal tract (GIT). In two additional treatment groups SBP60 was offered from a weight of either 36 kg or 72 kg before SBP80 was offered at 108 kg. Daily live-weight gain, after allowing for the effects of a change of gut fill, was less at all weights on the high bulk foods than on C. At all weights the high bulk foods caused a significant increase in the weights of the stomach, large intestine, caecum and gut fill. Effects on the weight of the small intestine were small. Previous nutrition had no significant effect on the adapted performance, or on the size of the GIT, of pigs given SBP80 at 108 kg but pre-feeding SBP60 significantly increased initial consumption of SBP80. Constrained intake was not directly proportional to live weight beyond 40 kg. The absolute capacity for bulk (Cap, kg water-holding capacity per day) was related to live weight (W, kg) by the quadratic function Cap = (0·192.W) - (0·000299.W2). The value of Cap is predicted to reach a maximum when W = 321 kg. The combined weights of the large intestine and caecum (WLIC) changed with W in ways that were similar to the way in which Cap changed. In addition the ratio of Cap to WLIC was close to constant. The combined weight of the large intestine and the caecum may determine the capacity for food bulk in pigs.
The amount of a bulky food that an animal can eat depends on its capacity for bulk and the bulk content of the food. For pigs between 12 and 40kg the capacity for food bulk was found to be directly proportional to liveweight (Kyriazakis and Emmans, 1995). The way in which the capacity for bulky foods changes with weight above 40 kg is not clear; there is no a priori reason to assume that the scaling rule proposed for young pigs will hold in heavier pigs. The applicability of the work in young pigs for use in more mature pigs needs investigation, to develop predictive equations for the whole relevant weight range. An experiment was designed to determine how the capacity for bulk changed with weight; the objective was to develop a relationship between the capacity for food bulk and liveweight.
Current models that predict food intake over time assume that the animal is always fully adapted to the food that it is on. This approach does not account for the immediate effects of a change in food type upon intake. Such a change may have large effects on intake and performance particularly when the change is to a food of higher bulk content. Such a change initially causes a reduction in intake. Over time, with adaptation, intake gradually increases until a new equilibrium intake is reached. The ability to predict intake and performance during the period of adaptation will allow models to predict food intake on high bulk foods more accurately. Data recorded during the period of adaptation are frequently excluded, perhaps to make the prediction of intake on high bulk foods easier. This work is an attempt to develop a model to predict intake and performance during the adaptation period when an animal is changed to a food of higher bulk content.
The objective of this experiment was to provide a severe test of the two frameworks currently available for understanding and predicting voluntary food intake. Framework 1 predicts that an animal will eat at a level that will allow potential performance to be achieved subject to its capacity to deal with a constraint, such as the bulk content of the food, not being exceeded. In framework 2 intake is seen as that which will allow some biological efficiency, such as the ratio of net energy intake per litre of oxygen consumed, to be maximised (Tolkamp and Ketelaars, 1992). The frameworks differ in their prediction of the effect that a period of prior feeding on a high bulk food (severely limiting) will have upon the subsequent intake of foods of differing bulk content. Framework 1 predicts that the intake of a low bulk food, that is non limiting, but not that of a moderate bulk food, that is limiting, will be increased under such circumstances. Framework 2 predicts that intake will be increased regardless of the type of food being fed as long as the Metabolisable Energy of that food is utilised more efficiently.
The effect of a period of feeding on a high bulk food, upon the subsequent intake of foods of differing bulk content, was investigated in two experiments of the same design. The intention was to provide a severe test of the two current conceptual frameworks available for the prediction and understanding of food intake. In each experiment 40 male Manor Meishan pigs were randomly allocated to one of four treatment groups at weaning. Each experiment was split into two periods, P1 (12 to 18 kg) and P2 (18 to 32 kg). The treatments, all with ad libitum feeding, were: a control food (C) given throughout (treatment CC); a medium bulk food (M) given throughout (treatment MM); a high bulk food (H) given in P1 and then C in P2 (treatment HC); H given in P1 and M in P2 (treatment HM). C was based on micronized wheat with 13·4 MJ digestible energy and 243 g crude protein per kg fresh food. In experiment 1 M contained 350 g/kg and H 560 g/kg of unmolassed sugar-beet pulp and in experiment 2 M contained 500 g/kg and H 700 g/kg of unmolassed sugar-beet pulp. Framework 1 predicted that food intake on the medium bulk food (M) would not be increased, whereas framework 2 predicted that intake on M would be increased after a period of feeding on H, compared with when M was offered continuously.
In P1, both food intake (P < 0·01) and growth (P < 0·001) were severely limited on H compared with C. In experiment 1 growth was limited on M compared with C during the first 7 days of P1 (P < 0·01) only. In experiment 2 intake (P < 0·001) and growth (P < 0·001) on M were limited throughout P1, compared with C but not thereafter. Therefore, in neither experiment did M cause a lower growth rate than C from 18 to 32 kg. In experiment 1 there was full adaptation to M after about 10 days from 12 kg. In experiment 2 adaptation was complete by the end of the first 7 days from 18 kg.
In P2, food intake (P < 0·001) and live-weight gain (P < 0·05 and P < 0·001 in experiments 1 and 2, respectively) were increased on HC compared with CC. By the last 7 days of P2 intake was still higher (P < 0·01) but growth rate was no longer different to CC. Intake and gain were increased in P2 on HM compared with MM but, in general, these differences were small and not significant. In the first 7 days of P2, in experiment 1 pigs on HM had higher intakes (P < 0·001) and gains (P < 0·05) than those on MM, but in experiment 2 only intake was higher (P < 0·01) with no difference in gain. By the last 7 days of P2 there was no difference in either intake or gain between these two groups in either experiment. Pigs on HC increased intake by more than those on HM. There was, therefore, a significant interaction for food intake (P < 0·05, in experiment 1 and P < 0·001, in experiment 2) between prior and present food.
The unexpected failure of either M food to limit growth throughout the experimental period meant that the results of these experiments could not be used as a strong test to reject either one of the frameworks. However, the ability of the pigs to compensate on M was less than that on C. The data provide some evidence that under conditions of compensation foods such as M may be limiting. This is in closer agreement with the framework that predicted that consumption of a limiting food will not increase after a period of feeding on a high bulk food (framework 1).
Currently there are two theoretical frameworks for the prediction of feed intake of animals. The first considers feed intake to be a consequence of the animal eating to achieve its genetic potential (Kyriazakis and Emmans, 1999). When potential performance is not achieved it is because feed intake is being constrained, for example through the bulkiness of the feed or the hotness of the environment. The second framework considers feed intake to be an outcome of some process of optimisation so that intake is that which allows the maximisation of biological efficiency (Tolkamp and Ketelaars, 1992). The two frameworks differ in their predictions of the effect of temperature on the intake of bulky feeds. In the first, feed intake on bulky feeds is seen as a function of the type of feed; in the second, feed intake is a function of both the type of feed and the environment. The first framework predicts that in the cold the intake of low, but not high, bulk feeds will increase. The second framework predicts that in the cold intake will be increased regardless of the type of feed offered. This experiment was designed to provide a severe test of the two feed intake theories.
Email your librarian or administrator to recommend adding this to your organisation's collection.