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Protein & Pregnancy

Protein, Pregnancy and Progesterone ....& Feed Intake?

Literature review for Australian White Suffolk Association

As a breed society that relies heavily on AI as a means of distributing elite genetics, we have long been frustrated by the seemingly unexplained variability of conception results. As a breed we held a forum at our 2009 Annual Conference in Albury to try and gain a consensus of what generally works to achieve high conceptions. The best we could evaluate from this forum is that what works for one breeder, does not necessarily ensure success for another. It is well known that around 20-30% of embryos fail within the first weeks of pregnancy so we need to focus on retaining what remains viable. So we are none the wiser as to how to ensure an acceptable conception rate through the use of AI.

One common thought in relation to conception is the effect of high levels of protein post AI and the negative effect this has on embryo survival. It has been well documented in many research programs that diets excessive in protein increase plasma urea nitrogen (PUN) concentrations in the blood which in turn have a toxic effect on both the oocyte and embryo leading to lower levels of fertility and conception. High protein intake is also linked to unfavourable changes in the environment within the uterus and decreased progesterone secretion, both of which have a negative impact on conception. However there is a level of contradiction within these trials ranging from little effect to a massive reduction in conception and as Progesterone is the “hormone of pregnancy”; much of the research has been focussed around circumstances that affect levels of progesterone during and after conception.

In the trials where high protein diets that were associated with negative energy balance and heat stress the conception rates were even lower, whereas when protein and energy were more in balance the effect was not as dramatic or not significant. So what role does energy balance or feed intake have on the rates of conception post AI?

Research conducted by Parr (1992) compared the rates of conception across a range of feed intake levels with some interesting results. He found that ewes fed twice their maintenance ration of energy during early pregnancy had a significant reduction in conception rates; 48% compared to ewes fed their maintenance ration with a conception rate of 68%. Ewes fed only half the maintenance energy requirement had no reduction in conception. If the ewes receiving the higher maintenance ration were administered progesterone during the first weeks post joining, their conception rates increased to 76%, indicating that the higher feed intake or twice the maintenance ration was having a significant effect on progesterone levels causing embryo death.

Blood tests indicated that the levels of Progesterone were inversely proportional to the level of feed intake and the most sensitive period for the embryo was 11-12 days after mating. Another finding was that the blood flow from the Portal Vein (Stomach to Liver) was directly related to feed intake and as the Liver is efficient in removing 96% of Progesterone, the higher the feed intake, the lower the blood level of Progesterone and given that the Corpus Luteum could not maintain the higher levels of Progesterone required to maintain a balance, the embryo is at risk.

So is it the level of protein that creates a problem with conception or is it the level of energy intake? Research would indicate both. There is little doubt from many research projects that high protein diets create an unfavourable environment for the new embryo and indeed the unfertilised egg. We also know that diets containing high levels of energy (twice the maintenance level) will result in lower levels of Progesterone resulting in embryo loss. If we assume that the good managers of sheep enterprises may over compensate feed intake to allow for lower protein levels, this could well explain some of the variability we see with AI programs. Putting the AI ewes on the best feed after insemination may well be the problem and it seems that day 11-12 after insemination is the crucial time. If Progesterone levels are low at this time the chances of embryo survival is significantly decreased. It is worth noting that even a diet at half the daily maintenance energy levels, no adverse loss of embryos was recorded when compared to the full maintenance level diet over the first 2 weeks post conception.

Although this work was carried out a few years ago, there is further research currently being carried out to further evaluate the effects of feed intake and the association with Protein on embryo survival after an AI program.

Just another variable to add to the challenges of getting good results from AI.


Parr, R A   Nutrition – Progesterone Interactions during early Pregnancy in Sheep,           Reprod. Fertil. Dev. (1992), 297-300

Rhoads, M L et al   Effects of Nutrient Metabolism and Excess Protein Catabolism on Dairy Cow Fertility