Conjugated Linoleic Acid and dairy cows: metabolism, reproduction and products quality.
[Tesi di dottorato]
The aim of this dissertation was to evaluate in dairy cows the effects of the supplementation of Conjugated Linoleic Acid, as natural feed (pasture) or as additive (CLA rumen protected), on quality of dairy products and on cow metabolism and reproduction.
In the first experiment three farms of the Alta Irpina area, (Campania region, Italy) were surveyed focusing on three main features
In the farms surveyed, cows’ requirements were seldom met due to the poor quality of the forages, the not-rational use and exploiting of natural resources and the inadequate lactating cow management. Essentially the farms in this area need to be supported by technical assistance services that could reduce the production costs and improve the milk productions.
Pasture management and improvement really represent a critical point that may lead negative or positive consequences on the economic vitality of the territory and product quality. Some practical advices for pasture management are related to weed control, rotational grazing, use of fertilizers, and introduction of herbs. However to improve the pasture quality, it’s needed to take in account the geological and climatic characteristics of the area and to act by little inputs to avoid loosing of efforts in a not really responsive territory.
The problem highlighted about milk production was, mainly, still related to an incorrect livestock management. As regard milk quality, beside the somatic cells count, it resulted satisfying. The higher count of somatic cells, probably due to the poor hygienic conditions during the milking process, can affect milk yield and quality.
As regard cheese quality, pasture feeding positively influenced the acidic profile of the Caciocavallo cheeses that presented higher level of CLA and PUFA, higher percentage of butyric acid and lower content of palmitic acid. This result represents a straight for Alta Irpinia territory as it could allow to improve the profitability of dairy farms and also it helps to preserve and to enhance the pastures areas.
Feeding factors, in fact, make it possible to vary milk FA composition in many ways. Recent advances in the knowledge of FA synthesis mechanisms (digestion and metabolism) and their putative physiological effects in human consumers have significantly boosted ongoing research and potential applications. As regards ruminant nutrition, the aim, for dairy farmer of Alta Irpinia, should be to better understand the effects and better use grass-based diets
From the sensory test on the caciocavallo cheeses, the only differences noticed were related to the cheese making farm more than to the feeding. These differences also if not really strong, don’t allow the characterization of the products.
In conclusion, it can be affirmed that the dairy system of Alta Irpinia area, if technically supported, has a high potential for improvement.
Overall our results constitute objective data for dairy farmer of Alta Irpinia area, as they refer back to the measures to be taken to update or maintain certain feeding conditions (i.e. maintenance of pasture) so that dairy products best reflect the uniqueness and diversity of the native land where they are produced.
In the second experiment the effect of dietary rumen protected CLA on metabolism and reproduction of dairy cows from an intensive farm system in USA was evaluated on the basis of the following remarks.
In the intensive systems, during the last decades, a lot was done to increase milk production. However, this increase in milk output per cow has been accompanied by a worldwide decline in cow fertility. High-yielding dairy cows are typically in a state of negative energy balance postpartum. Insufficient energy supply results in poor reproductive performance. Fat supplementation in early lactation may improve reproduction because it can increase energy density of the diet resulting in an improvement in energy balance. In addition, certain unsaturated fatty acids may impact reproduction because they can modify metabolism and gene expression.
Considering the results obtained, they indicated that CLA treatment did not affect milk production and quality; only milk fat decreased progressively over the experimental period in the treated cow. As regard milk fatty acid profile, in treated group significant increments were observed for CLA cis-9, trans-11 and trans vaccenic acid, the main precursor of cis-9, trans-11 CLA. No differences were observed for C18:1 trans 10, acid correlated to Milk Fat Depression (MFD) and CLA trans-10 cis-12. Moreover palmitic acid (C18:6) showed lower value in CLA treated group.
Treated cows had an higher intake during the prepartum period and a reduced intake postcalving (P<0.01). This particular trend might be due to the fact that the fatty acid supplement from the prepartum period reduced the negative cow energy balance in postpartum period.
Plasmatic and follicular LDL tended to be higher in treated group whereas no differences were observed for Cholesterol and HDL neither in plasma or follicular fluid.
A positive relationship, althought not significant, between GH and IGF receptors was observed in treated cows. Also, the assumption of equal variance was violated in the group supplemented with CLA that shows an higher variability of the response and a numerical tendency to higher values regarding GH and IGF-I receptors This trend, althought not justified statistically could let allow to suppose that by using a larger number of samples an improvement of GH and IGF-I receptor could be shown.
Moreover, in a subsample of cows the glucose level was mesured during the day and the cows supplemented with CLA showed a tendency to lower levels of glucose compared with the control. Since higher levels of IGF-I were reported in cows treated with CLA supplementation, these results might be related to higher levels of insulin and, therefore, to higher levels of IGF-I also in the blood. This hypothesis might allow to hypothesize a direct action of the CLA in the liver.
The level of estradiol tended to be higher in the CLA group as LDL concentration in blood. Since granulose cells use LDL to produce Progesterone in the luteal phase, this result might explain the reason of higher level of progesterone observed in previous studies. Moreover, further analyses are needed to confirm this result.
In conclusion, the data presented in the second experiment suggest that including CLA in the diet can modify endocrine signals that may potentially benefit reproductive outcome. Moreover, studies with larger number of cows are needed to definitively corroborate the effect of CLAs on fertility.
However, milk fat production, from day 60 in milk started to be lower in the group supplemented with CLA. This “negative” effect, also if thought as a way to approach the negative energy balance of cows could lead the farmer to avoid the use of this kind of supplementation. For this reason, taking in account the effect of CLA on milk production, considering the opportunity to develop nutritional strategies might be useful to establish the optimal daily dose to use and the optimal supplementation program to best use CLA supplementation as improving products quality and fertility.
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