ARTIFICIAL INSEMINATION IN FARM ANIMALS - Phenix-Vet

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224Artificial Insemination in Farm Animalsindirectly through prostaglandins. STAR plays a fundamental role in the synthesis of steroidhormones (Stocco et al., 2005). In previous work, it has been observed that in beef heifersthere was a reduction in the concentration of arachidonic acid in the endometrial tissuewhen they were fed n-3 PUFAs (Childs et al., 2008a; Childs et al., 2008b). On the other hand,there is evidence that supplementation with linoleic acid (n-6) increased uterine secretion ofPGF 2α (Cullens, 2005), which could derive in a greater availability of arachidonic acid in theendometrium. Under such conditions it could be speculated that a possible way to act of then-3 and n-6 fatty acids in steroidogenesis is by reducing or increasing the availability ofarachidonic acid, respectively and as a consequence, the expression of RNAm for STARsynthesis.3.2 Lipids on ovarian activityThese results suggest that another of the mechanisms by means dietary lipids may improvereproductive performance of cattle is influencing follicular development and ovulation. Inthis, respect, Lucy et al. (1991), replaced corn with Ca-LCFA from palm oil in the ration ofdairy cows at calving, and increased the number of medium size follicles (6-9 mm) and offollicles greater than 15 mm within 25 days postpartum. Furthermore, the diameter of thegreatest follicle was superior in cows fed Ca-LCFA from palm oil (18.2 vs 12.4 mm). Whenthis study was repeated with isocaloric diet, observed effects were similar (Lucy et al. 1993).The greatest increase in medium follicle populations occurred in response to plant oilconsumption, which is likely a direct result of the effects of high levels of linoleic acid in therumen. Maximum follicular growth responses to plant oil supplementation have occurredwhen plant oils were fed at 4 to 6% of dietary dry matter, with lesser increases observed atlower levels of added fat. Animal tallow, calcium salts of saturated fatty acids or fish oilhave been shown to have less clear effects on follicular growth than plant-derived oils.Moreover, postpartum beef cows which calved in a very poor body condition (BCS of 3; 1-9scale) were unable to develop medium or large follicles at a rate equal to those with a bodycondition score of 4 or greater after 3 weeks of fat consumption (Ryan et al., 1994).The number of medium size follicles (5 to 10 mm) was higher in beef cows which consumedfeed with a greater content of PUFAs (Thomas et al., 1997) and in dairy cows whichconsumed a diet enriched with 5% n-3 fatty acids derived from fish oil (Heravi-Moussavi etal., 2007). Similar results were observed in cows fed with diets enriched with n-3 or n-6 fattyacids (Robinson et al., 2002). Staples & Thatcher (2005) summarized the effect of increasinglipids in the ration on the size of the dominant follicle: on average, the size of the dominantfollicle was 3.2 mm greater than in females fed with some source of fat, which represents a23% increase. Other studies (Bilby et al., 2006d; Garnsworthy et al., 2008) showed that thesize of the dominant follicle is increased in cows fed diets rich in PUFAs. In sheep, the use ofCa-LCFA from palm oil (El-Shahat & Abo-El maaty, 2010) or from corn oil (Herrera et al.,2008) in the feed improved the number and size of the preovulatory follicles, as well as rateof ovulation and the superovulatory response in Pelibuey sheep (Herrera et al., 2008). Theseevidences demonstrate that consumption of lipids accelerate follicular growth (de Fries etal., 1998), which may influence the restart of ovulation postpartum, as it was shown byMarín-Aguilar et al. (2007) who observed that Holstein cows supplemented with plant oil(60% PUFAs) reduced by 7 days the restart of ovarian activity relative to a control group. de<strong>Vet</strong>h et al. (2009) observed that time at first ovulation in dairy cows was reduced by 8 dayswhen they were supplemented with 8 g/d of trans-10, cis-12 CLA.
Effect of Fatty Acids on Reproductive Performance of Ruminants 2254. Lipids and its effect on endometrial secretion of prostaglandinsStudies in a variety of species have shown that dietary PUFAs can modulate prostaglandinsynthesis and metabolism. Eicosanoids, comprising prostaglandins, thromboxanes,leukotrienes and lipoxins, are all synthesized from C20 fatty acids (Mattos et al., 2000). Themost biologically active two series prostaglandins are derived from arachidonic acid, but theless active three series prostaglandins can be produced from eicosapentaenoic acid by theaction of the same enzymes (Robinson et al., 2002).Prostaglandins play an important role in reestablishing oestrus cycles both immediatelyafter parturition and thereafter until conception. Prostaglandin F 2α (PGF 2α ) is responsible foruterine involution after parturition. The uterus releases PGF 2α during each oestrus to regresseach new corpus luteum if the cow is not pregnant and initiate a new oestrus cycle. Duringthe period of corpus luteum regression, concentrations of PGF 2α and progesterone areinversely related. If the cow does conceive, release of PGF 2α from the uterus is prevented inorder to preserve the corpus luteum and maintain pregnancy (Funston & Filley, 2002).Linoleic acid is a substrate for the synthesis of PGF 2α . Linoleic acid can be desaturated andelongated to arachidonic acid (C20:4, n-6), which is a precursor for PGF 2α . Regulatoryenzymes for this conversion include delta 6 desaturase and cyclooxygenase. Linoleic acidcan inhibit prostaglandin synthesis by competitive inhibition with these key enzymes.Arachidonic, and two fatty acids found in fishmeal, eicosapentaenoic (C20:5) anddocosahexanoic (C22:6), have been shown to inhibit cyclooxygenase activity as well. It isimportant to note that linolenic acid (C18:3) was also present in the endometrialprostaglandin synthesis inhibitor isolated by Thatcher et al. (1994), and that linolenic acidhas been shown to be a strong inhibitor of prostaglandin synthesis (Mattos et al., 2000). Theamount and probably type of particular fatty acids reaching the target tissues likelyinfluence if prostaglandin synthesis is going to be stimulated or inhibited (Thatcher &Staples, 2000).Figure 1 shows the schematic metabolic pathway of dietary n-6 and n-3 PUFAs andpotential mechanisms for regulation of PGF 2α secretion. Absorbed PUFAs are desaturatedand elongated in organs such as the mammary gland, adipose tissue, testis, brain, placentaand the liver (of non-ruminants). Dietary PUFAs and their desaturation and elongationproducts are incorporated into phospholipids of the plasma membrane. The amount of eachfatty acid incorporated depends on the amount of precursor present in the diet. Externalstimuli such as the binding of oxytocin (OT) to the oxytocin receptor (OTr) stimulates theactivity of phospholipase A2 (PLA2) and phospholipase C (PLC), which cleavephospholipids from the plasma membrane and ultimately increase availability ofdiacylglycerol (DAG) and fatty acids for processing by prostaglandin H synthetase (PGHS).Eicosapentaenoic acid (EPA; C20:5, n-3) is processed by PGHS to generate prostaglandins ofthe 3 series. Arachidonic acid (AA; C20:4 n-6) can be processed by PGHS, epoxygenase andlipoxygenase to generate prostaglandins of the 2 series, epoxyeicosatrienoic acids (EETs),leukotrienes and hydroxyeicosatetraenoic acids (di-HETEs), respectively (Mattos et al.,2000).In vitro studies have demonstrated that some n-3 (eicosapentaenoic and docosahexaenoic)fatty acids reduce biosynthesis of prostaglandins of the series 2 in cells and tissues (Mattoset al., 2003). Similarly, some isomers from conjugated linoleic acid inhibited synthesis ofPGF 2α and the effect was independent of the concentration of linolenic acid and the ratio n-6:n-3 (Harris et al., 2001). The above results are interesting due to the fact that most
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ARTIFICIAL INSEMINATION IN FARM ANIMALS - Phenix-Vet

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