Great Lakes Dairy Sheep Symposium - the Department of Animal ...
Great Lakes Dairy Sheep Symposium - the Department of Animal ... Great Lakes Dairy Sheep Symposium - the Department of Animal ...
that, whereas only half of the models include food factors, all models include animal factors as independent variables, in that they influence nutritive requirements. If body weight changes, then so does intake. This is connected to the basal metabolism that affects requirements, and to rumen volume. One empirical method which is very widely used to predict the intake capacity of ruminants is to calculate it as a percentage of the body weight (for sheep about 4 to 5.5% of BW). The correlation between the body weight of different genetic types and the intake of adult sheep is clear (Table 5). The same tendency is not always observed, however, when the regression within each genetic type is analysed. Indeed, one can say that in this case, because an increase in weight over the normal mature weight is an index of fattening, intake tends to diminish (Forbes, 1995). Table 5 - Dry matter intake and body weight in various sheep breeds (Avondo and Lutri, 2004). Breed Frisona orientale Lacaune Chios Delle Langhe Manchega Massese Comisana Churra Sarda Body weight kg 74.8 73.2 60.0 58.0 57.0 52.4 57.4 50.0 42.2 96 DM intake kg/day head -1 2.49 2.67 2.24 1.83 2.24 1.98 1.99 1.83 1.55 When pasture conditions are favourable, intake is positively correlated with productive level. However, literature highlights the great variability of this correlation coefficient, with values ranging from 0.2 to 0.8 (Serra, 1998). This variability depends on the stage of lactation. There is a phase when the ewes satisfy their increased nutritional requirements by mobilizing fat reserves. Any attempt to estimate the intake capacity of lactating ewes should therefore take into account their physiological tendency to mobilize body reserves in the early months of lactation and then later to restore them. This means that the fall in intake in the phase after the lactation peak may not always be as marked as expected. Various experiments (D’Urso et al., 1993; Pauselli et al., 1993; Pulina et al., 1992; Trimarchi et al., 1981) on dairy sheep during lactation have found falls in intake lower than 20% while the corresponding falls in milk production were higher than 65% (Table 6).
Table 6 - Dry matter intake and milk production of ewes (Avondo and Lutri, 2004). Intake Lactation week Breed g DM day -1 Milk production g day -1 3 Comisana 2670 2026 Pauselli et al.,1993 8 2634 1025 14 2149 693 7-9 12-14 16-18 6 10 14 18 5 from dry 4 from dry 3 from dry 2 from dry 1 from dry Massese Comisana Sarda 2200 2200 2050 1323 1373 1820 1428 2539 2079 2521 2042 2153 97 1068 588 346 1077 783 488 424 1095 1005 976 856 721 Trimarchi et al., 1981 D’Urso et al., 1993 Pulina et al., 1992 Given the above, the following equation has been developed to predict intake in Italian milk breeds (Pulina et al, 1996). It takes into account not only the weight and milk production of the animal, but also daily weight changes. In adult animals these can occur through the animal storing or mobilising its body reserves: [3] I = -0.545 + 0.095 MW + 0.65 FPCM + 0.0025 BWC where: I = DM intake, in kg/head day -1 ; MW = metabolic weight (BW 0.75 ), in kg; FPCM = fat (6.5%) and protein (5.8%) corrected daily milk production, in kg (Pulina et al., 1989) BWC = body weight changes, in g day -1 . Pasture characteristics Predicting the feed intake of grazing sheep is much more complex than it is for sheep fed indoors. If animals have free access to pasture, their selective grazing behaviour can significantly modify their intake capacity. This selection is very important, not only for the quality of the diet but also for the herbage intake. In fact, searching activity for the more appetising parts can limit intake more than forage availability does. It has been hypothesised (Arnold and Dudzinsky, 1978; Forbes and Provenza, 2000; Provenza, 1995) that sheep use a sort of selective "wisdom" when selecting. This minimises metabolic discomfort and allows the animals to eat feed according to their nutritional requirements and also to discard toxic matter. Sheep tend to select a diet more digestible and richer in crude protein than the available herbage. Moreover, this
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Table 6 - Dry matter intake and milk production <strong>of</strong> ewes (Avondo and Lutri, 2004).<br />
Intake<br />
Lactation week Breed g DM day -1<br />
Milk production<br />
g day -1<br />
3<br />
Comisana 2670<br />
2026 Pauselli et al.,1993<br />
8<br />
2634<br />
1025<br />
14<br />
2149<br />
693<br />
7-9<br />
12-14<br />
16-18<br />
6<br />
10<br />
14<br />
18<br />
5 from dry<br />
4 from dry<br />
3 from dry<br />
2 from dry<br />
1 from dry<br />
Massese<br />
Comisana<br />
Sarda<br />
2200<br />
2200<br />
2050<br />
1323<br />
1373<br />
1820<br />
1428<br />
2539<br />
2079<br />
2521<br />
2042<br />
2153<br />
97<br />
1068<br />
588<br />
346<br />
1077<br />
783<br />
488<br />
424<br />
1095<br />
1005<br />
976<br />
856<br />
721<br />
Trimarchi et al., 1981<br />
D’Urso et al., 1993<br />
Pulina et al., 1992<br />
Given <strong>the</strong> above, <strong>the</strong> following equation has been developed to predict intake in Italian<br />
milk breeds (Pulina et al, 1996). It takes into account not only <strong>the</strong> weight and milk production <strong>of</strong><br />
<strong>the</strong> animal, but also daily weight changes. In adult animals <strong>the</strong>se can occur through <strong>the</strong> animal<br />
storing or mobilising its body reserves:<br />
[3] I = -0.545 + 0.095 MW + 0.65 FPCM + 0.0025 BWC<br />
where:<br />
I = DM intake, in kg/head day -1 ;<br />
MW = metabolic weight (BW 0.75 ), in kg;<br />
FPCM = fat (6.5%) and protein (5.8%) corrected daily milk production, in kg (Pulina et al.,<br />
1989)<br />
BWC = body weight changes, in g day -1 .<br />
Pasture characteristics<br />
Predicting <strong>the</strong> feed intake <strong>of</strong> grazing sheep is much more complex than it is for sheep fed<br />
indoors. If animals have free access to pasture, <strong>the</strong>ir selective grazing behaviour can significantly<br />
modify <strong>the</strong>ir intake capacity. This selection is very important, not only for <strong>the</strong> quality <strong>of</strong> <strong>the</strong> diet<br />
but also for <strong>the</strong> herbage intake. In fact, searching activity for <strong>the</strong> more appetising parts can limit<br />
intake more than forage availability does. It has been hypo<strong>the</strong>sised (Arnold and Dudzinsky,<br />
1978; Forbes and Provenza, 2000; Provenza, 1995) that sheep use a sort <strong>of</strong> selective "wisdom"<br />
when selecting. This minimises metabolic discomfort and allows <strong>the</strong> animals to eat feed<br />
according to <strong>the</strong>ir nutritional requirements and also to discard toxic matter. <strong>Sheep</strong> tend to select<br />
a diet more digestible and richer in crude protein than <strong>the</strong> available herbage. Moreover, this