I have a herd that dropped from 3.8% fat to 3.4% over the last few weeks. There have been no diet changes except there has been heat stress. RUFAL on the herd is low at 2.16%. Milk is running about 89 pounds. Larry Jones did a milk fatty acid analysis and found 0.75% de novo, 1.20% mixed and 1.23% preformed fatty acids which indicates that the problem is not a CLA effect but a substrate effect. They are all equally low. The diet has 0.65 lbs of Palmit 80. This is a high by-product herd with a little corn silage (19 lbs), Ryelage (3 lbs) and straw (0.5 lbs). The starch is running 26% with 5% sugars. Any ideas why fat would drop this much this fast?
Need more diet info. You said 22.5 lbs of rye, straw and corn silage. What is NDF 30 and uNDF 30 and u NDF 240?. What is in the other 33 some lbs. Thanks
The purpose of Anonymous Post is to protect the nutritionist from many angles. Consequently, the user that is posting may choose to route the answers to questions to me. As in this case, I have the rations and will respond to keep the herd anonymous. We are hoping that this system will encourage user to share herd information which they might not if it is tagged with a nutritionist. The NDFu30 is low at 3.95 lbs and the NDFd30 is also low at 4.9 lbs. This is made up with citurs, soy hulls, wet brewers.
Dave is correct the diet details are key to sorting out the cause/solutions to this MF drop. However I want to emphasize what Larry Jones stated clearly in his FARME Institute Newsletter circulated today. He states, “A seasonal effect on milk fat is well documented in many regions of the world”…[you can read]…”and this becomes a strong downward spiral.”
The point here is that summer time MF depression is not unusual. I’d admit 3.8 to 3.4 is a big drop but how fast? Are we talking about days, weeks, months. I’ve tracked milk fat lbs and % in about 16,000 cows for about the past 10 years. We lose about .3% and .27 lbs of fat EVERY summer. What has been the history in this herd? Have they historically lost MF in the summer? It is easy to forget what happened last year and the years previous. If you track those data it makes the pain associated with a 3.8 to 3.4 drop a little less painful.
What region is the farm in?
We have several dairies in West Central MN and Eastern SD. Many of our farms experienced a dramatic drop in fat % in the 2-3 weeks after Memorial Day, in the 0.15-0.20 range. Some herds are Jersey/crossbred and some are primarily Holsteins. It was quite alarming at the time but when I graphed all the sites’ fat % since January I found that they all had a much slower rate of decline from January to May then what is normal or no change at all. The entire decrease from mid January to mid July is pretty close to normal, it just seems like the majority of the decrease happened in late May/early June. I’m not sure why this occured but the fact that February, March, and April temps were all well below normal while May (especially the 2nd half) and June were well above normal is probably a factor.
The best I can tell you is the herd is in the Southeast. I don’t want to get more specific then that.
For the NE data, the biggest drop is May and June. The rise is a bit slower across Sept, Oct, and Nov. It seems to be related to the rate of day length change. July/August is flat and around the winter solstice (Dec, Jan, Feb, Mar, April) is flat.
I agree with the previous comments, taken in isolation a 3.4% milk fat with 89 lb in the SE in Jul is not too shabby. I wouldn’t think. But that observation may not make the producer feel any better or answer why the sudden and dramatic drop.
The following is Jim Aldrich thinking out load (dangerous) and is subject to debunking by anyone who would like to weigh in:
I think swings in milk fat, in additional to being affected by the usual dietary suspects, have a connection to insulin and insulin sensitivity (or insulin resistance). Lance Baumgard’s heat stress work at Iowa State showed that heat stressed cows lost more milk than pair fed thermal neutral cows (cows that were kept at the same lower intake as the heat stressed cows). Heat stressed cows had higher insulin sensitivity than pair fed controls. The latter were more metabolically flexible and were able to mobilize fat to support lactation whereas the heat stressed cows did not. This study and others were focused on heat stress effects on milk production, intake and health (leaky gut, LPS etc) and not specifically designed to look at milk components. However if we think about cows under heat stress being insulin sensitive and less able to mobilize fatty acids (FA) when intake drops, then there is going to be less preformed FA available for milk fat synthesis. Interesting in this case palm fatty acids were being fed and see McFadden’s work on Ceramide (Cornell Nutr. Conf., 2017) and C16:0 is a precursor to ceramide and ceramide actually enhances insulin resistance. So was there a metabolic battle being waged in these cows whereby diet treatments were encouraging insulin resistance (and providing FA for milk fat and stimulating MF synthesis) that was finally overwhelmed by insulin sensitivity caused by heat stress? Sounds a bit wacky to me but that’s what I got.