High Feed Intake May Be Affecting Your Reproduction

Dr. Allen Young
USU Extension Dairy Specialist
I don’t think it is a surprise to anyone that reproduction in dairy cows has been deteriorating over the last several years. While some of the negative effects can be managed, there still seems to be some type of physiological reason that cows are not getting pregnant. Researchers from the University of Wisconsin recently reported on a physiological reason that could account for some of these reproductive problems. The article is found in the Journal of Dairy Science, volume 85(11), page 2831 (2002). The answer may be as simple as a change in liver metabolism of steroids.

Lactating cows (average milk yield was 83.6 lbs) were divided into four groups: unfed, fed 0.5 maintenance level (M), 1.5 M and 2.2 M, then monitored for four hours after feeding. Dry matter intakes for the four hour period were 0, 7.8, 23.4, 33.5 lbs, respectively. Average liver blood flow for these time periods is shown in Table 1. Serum concentrations and metabolic clearance rate of progesterone are shown in Table 2.

Table 1. Liver blood flow after feeding for different levels of feed intake based on maintenance level.

Hour(s) after feeding	Liver Blood Flow (liters/h)
	Unfed	0.5 M	1.5 M	2.2 M
Serum progesterone concentration (ng/ml)
0	1561	1577	1572	1521
1	1574a	1816**b	1897**b	1937**b
2	1527a	1765*b	1871**bc	2017**c
3	1583a	1711*a	1835**ab	1967**b
4	1547a	1685ab	1817**b	1984**c

* indicates differences within column; ^a,b,c Indicate differences within row.
The results suggest that liver blood flow increased after feeding, and the blood flow increased as feed intake increased. As feed intake increased, the length of time that liver blood flow was elevated increased. During this same time period, plasma levels of progesterone decreased because the rate at which the liver removed progesterone from the body increased. As with the blood flow, clearance of progesterone by the liver was elevated for a longer period of time when feed intake was increased. The liver removed the approximate equivalent of about 57% of the plasma levels of progesterone. They suggest that other organs of the body such as kidney, brain, ovary and adrenal glands metabolize the rest (Note: I would also add that the mammary gland is a source of removal of progesterone, as it is metabolized and secreted in the milk. As intake increases, milk yield also increases, removing a larger amount of progesterone).

In addition to progesterone, the study also looked at the effects of feeding level on estrogen removal from the body. They found the same results for estrogen as progesterone. The only difference was that liver metabolism of estrogen accounted for about 88% of estrogen removal in fasted and 71% in well-fed cows. This suggests that the liver is the primary source of removal of estrogen from the body.

The decrease in circulating levels of progesterone and estrogen could result in decreased fertility, increased pregnancy loss, reduced expression of heat, and possibly even double ovulations leading to twins. While I don’t advocate reducing dry matter intakes in cows, the increased blood flow to the liver can have major effects on reproduction. Increased management to overcome these deficiencies, such as supplementing progesterone, might be worth considering.

Table 2. Serum progesterone concentration and metabolic clearance rate after feeding for different levels of feed intake based on maintenance level.

Hour(s) after feeding	Unfed	0.5 M	1.5 M	2.2 M
Serum progesterone concentration (ng/ml)
0	2.59	2.60	2.58	2.59
1	2.69a	2.37*b	2.40b	2.32*b
2	2.76a	2.25**b	2.02***b	2.19**b
3	2.58a	2.35*a	1.95***b	1.96***b
4	2.59a	2.37*a	2.18**ab	2.01***b
Metabolic clearance rate of progesterone (liters/hour)
0	2881	2830	2838	2836
1	2753a	3226*b	3025ab	3138b
2	2669a	3295**b	3717***c	3324**b
3	2843a	3178*a	3801***b	3771***b
4	2804a	3066a	3409**ab	3692***b
Metabolic clearance rate of progesterone (liters/min/kg metabolic body weight)
0	0.374	0.366	0.369	0.367
1	0.357a	0.416*b	0.392ab	0.406b
2	0.345a	0.422**b	0.483***c	0.429**b
3	0.368a	0.408*a	0.493***b	0.489***b
4	0.364a	0.396a	0.443**ab	0.477***b

* indicates differences within column; ^a,b,c Indicate differences within row.