Supplying fat in dairy cattle rations has become a common practice on commercial dairies, as it is an effective way to supply
energy to the cow. In recent years, research has been conducted on different fat sources, more specifically on the types
of fatty acids provided through those various sources and their consequent effects on cow production, health, and reproductive
status. Two fatty acids, linoleic (C18:2, an omega-6) and linolenic (C18:3, an omega-3) have become a major focus of fat
research, as they are essential fatty acids (EFA) and must be supplied through the diet.
These EFA have double-bonds in their molecular makeup, and as such are susceptible to biohydrogenation by rumen microbes.
These microbes break the double bonds, resulting in the conversion of the EFA to stearic and other long-chain fatty acids
before the EFA can reach the small intestine for absorption. One means of avoiding biohydrogenation is to couple the EFA
with calcium salts of long-chain fatty acids (Ca-LCFA), effectively making the EFA rumen inert. This allows a larger portion of the EFA to reach the small intestine with double
bonds intact, and to be absorbed and circulated to virtually every tissue in the body (Schauff and Clark, 1992; Allred et
al., 2006). This paper will focus on the effects of EFA supplementation on hormone production, tissue repair and function,
and immune function of multiparous Holstein cows.
Role of EFA in hormone and prostaglandin production
Essential fatty acids are precursors to steroid hormones, via cholesterol. The corpus luteum (CL) uses cholesterol to produce progesterone (P
4
), and P4 itself is a precursor of estradiol (E), although it is an inhibitor of E secretion from follicles. Linoleic acid is also a proven inhibitor of cyclooxygenase
in endometrial tissues, and can subsequently suppress prostaglandin (PG) secretion from the uterus (Haag, 2001). Staples et al. (1998) state that this action might be aided by the effect fat has
in curbing E secretion, therefore further decreasing PGF2α production and reducing the sensitivity of the CL to PGF2α. Consequently, the life and functionality of the CL is extended and allows for increased P4 concentrations.
Progesterone is frequently referred to as the pregnancy hormone. The higher the concentration of P4 after conception, the greater the probability the animal will remain pregnant. Fonseca et al. (1983) and Shemesh et al.
(1983) both reported that higher pre-breeding P4 concentrations correlated linearly with increased conception rates. For each ng/mL serum [P4] increased on d 12 of the estrous cycle prior to AI, the conception rate improved 12.4% (Fonseca et al., 1983). Additionally,
Staples et al. (1998) cited that cattle with increased [P4] at the end of the estrous cycle demonstrated stronger signs of estrus. Stronger signs of estrus lead to more accurate head
detection and correctly timed breeding.
