Great Lakes Dairy Sheep Symposium - the Department of Animal ...

clearly further investigations of these effects are warranted. An analogous response has been
observed in lactating sheep when energy and nutrient supply were increased through the feeding
of a supplement composed of animal fat and rumen-protected methionine, and this resulted in an
increase in both milk yield and milk protein yield (Goulas et al., 2003). In addition, our study
demonstrated that the lactating sheep may represent an effective alternative model to elucidate
the mechanism of action by which CLA inhibits milk fat synthesis.
Considering that the majority of sheep milk is used to produce cheese, the effect of CLAsupplementation
on milk composition and how this may affect cheese yield and quality is of
commercial interest. The effect of milk composition on cheese yield and cheese quality was
recently reviewed at this conference (Wendorff, 2002). For most full-fat type cheeses the high
fat content of sheep milk is a disadvantage. A casein:fat ratio in sheep milk of 0.70-0.80 would
be desirable, however, this ratio is typically lower (0.55-0.65; Table 1), which results in excess
fat in sheep milk that typically is lost in the whey. In most cases, sheep milk would need to be
standardized by removing some milk fat in order to increase the casein:fat ratio to produce most
of the cheese varieties shown in Table 2. High losses of fat in the whey will result in a decreased
cheese yield. In our experiment described above, milk from sheep fed the unsupplemented
(control) diet had an estimated casein:fat ratio of 0.58, whereas this increased to 0.73 in milk
from CLA-supplemented animals, offering the potential to manipulate the diet in order to
improve cheese yield and quality. A further example where such a technology could be
employed is in the manufacture of Pecorino Sardo. This cheese is produced according to DOP
rules and according to those rules the milk cannot be skimmed (M. Griinari, personal
communication). A controlled reduction in the fat content of milk may allow for the production
of a better quality product, a reduction in the amount of fat lost in the whey, and an increase in
cheese yield. We have just completed a follow up experiment to investigate the effect of CLAsupplementation
on cheese yield and cheese quality. Milk from different treatments was made
into “cheddar” type cheese at the end of the experiment. The animal component of the
experiment has been completed and cheese manufacturing and assessment is underway; similar
reductions in milk fat content and yields were observed as described previously resulting in the
desired changes in the casein:fat ratio being achieved.
Table 1. Casein:Fat ratios for breeds of dairy
sheep. Adapted from (Wendorff, 2002).
Breed
Casein:Fat
ratio
Lacaune 0.60
Boutsico 0.60
Friesland 0.63
Italian Species 0.63
Current Expt. Control 0.58
Current Expt. CLA Supplemented 0.73
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Table 2. Ideal casein:fat ratios in
cows milk for commodity cheeses.
Adapted from (Wendorff, 2002).
Cheese
Casein:Fat
ratio
Cheddar 0.70
Mozzarella 0.85
Swiss 0.85
Parmesan 0.80
Havarti 0.60
Reduced Fat Muenster 1.73