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Fetal Programming & Sulfur Toxicity

Fetal programming from undernutrition can affect calf performance, producing lighter animals than their counterparts and impacting their performance in a feedlot system. High concentrations of sulfur can be toxic to cattle – decreasing performance and causing polioencephalomalacia.
Fetal Programming & Sulfur Toxicity

In this week's R2R Edition:

  1. Fetal programming from undernutrition can affect calf performance, producing lighter animals than their counterparts and impacting their performance in a feedlot system.
  2. High concentrations of sulfur can be toxic to cattle – decreasing performance and causing polioencephalomalacia, but the mechanisms of hydrogen sulfide production continue to be elusive.

Genetics

Undernutrition is underrated

The high-points:

  • Fetal programming is a term used to describe the effect that the mother's environment can have on the fetus during pregnancy.
  • Pregnant cows were given either 100% or 65% of their nutrient requirements for the first trimester.
  • Pirenaica calves from undernutrition cows were 16% and 14% lighter than their control counterparts at weaning and slaughter, respectively.

What you need to know: Fetal programming is a term used to describe the effect that the mother's environment can have on the fetus during pregnancy. When discussing this area of research, it is rarely concerning positive effects, as much of the concern is limiting the negative impacts on the pregnancy. One of these impacts is nutrition, or more accurately, the lack thereof.

The cows' nutritional requirements change depending on the animal's status, with different requirements open, pregnant, and lactating cows. The fetus may not have a high nutrient requirement during the first trimester of pregnancy compared to the latter two, but the lack of nutrition availability can impact foundational pregnancy development.

Researchers in Spain studied undernutrition's effect on fetuses, specifically the growth rate and meat quality characteristics of a calf born to an underfed cow during the first trimester. Cows were represented by Parda de Montaña and Pirenaica cattle breeds.

Cows were randomly assigned to one of the two treatments, the control group was fed 100% of their nutrient requirements, and the undernutrition group was fed 65%. These treatments continued for the first 81 days of pregnancy, followed by all animals receiving 100% of their requirements.

After birth, using only bulls from this point forward, the calves consumed their mother's milk exclusively and then were weaned at four months of age. The calves were entered into a feedlot and fed a typical high-concentrate feedlot ration until they were heavy enough for slaughter.

To say there was an impact of undernutrition is an understatement. Calves born to undernutrition cows had significantly lower weaning weights and slaughter weights. Specifically, the undernutrition Pirenaica bulls were 16% and 14% lighter than their control counterparts at weaning and slaughter, respectively.

Testicular development was significantly lower in the undernutrition calves as well as average daily gain. This is likely because the testicular growth rate is highly correlated to sexual maturity and, subsequently, sexual maturity with growth. Undernutrition appears to have impacted the height of the calves, where both undernutrition groups were shorter in stature than the control.

The Pirenaica calves from underfed cows had the greatest concentration of circulating free fatty acids (non-esterified fatty acids; NEFA). Additionally, the undernutrition animals had the greatest subcutaneous body fat. These elevated NEFA and high adipose levels demonstrate that the metabolic functions of the undernutrition calves have been altered and that more energy is being put towards adipose stores and less towards muscle.

Interestingly, each treatment group had similar intramuscular fat, even though the undernutrition Pirenaica calves had far more fat cover. Finally, all control calves had more tender meat than the undernutrition calves – however, all groups had moderate to low levels of tenderness in this study.  

Industry application: This study has demonstrated the impact of undernutrition on the fetus during the first trimester of pregnancy. These researchers bring to light the importance of ensuring cows have an adequate plane of nutrition during gestation and the costs it can bring to the operation if not.

Read more about it:

Long-term effects of early maternal undernutrition on the growth, physiological profiles, carcass and meat quality of male beef offspring
The effects of maternal undernutrition in early gestation on growth, metabolic and endocrine profiles, carcass and meat quality of male offspring in c…

Nutrition

The shifting solution for sulfur surplus symptoms

The high-points:

  • High concentrations of sulfur can be toxic to cattle, decreasing performance as well as causing polioencephalomalacia.
  • Cattle receiving additional sulfur were producing significantly more hydrogen sulfide.
  • There was no correlation between sulfur treatment and hydrogen sulfide production.

What you need to know: High concentrations of sulfur can occur in things like distillers grains, and water sources. Sulfur can be toxic to cattle, expressed as decreased performance and polioencephalomalacia (PMC). The emergence of PMC starts with the ruminal conversion of sulfur into hydrogen sulfide, then eructation of gases into the sinuses, and absorption of these gases into the vasculature around the nasal cavities. These gases cause neurologic damage and brain swelling.

However unpleasant and costly sulfur toxicity is, there is much that is not understood about the mechanisms which produce the hydrogen sulfide gas nor what could be done to control production. Sulfo-­reducing ruminal bacteria, or SRB for short, convert sulfur into hydrogen sulfide gas and are divided into two categories: assimilatory SRB (ASRB) and dissimilatory SRB (DSRB). A current hypothesis is that DSRB is the source of increases in hydrogen sulfide gases during high sulfur intake, which leads to polioencephalomalacia.

Twelve crossbred steers were separated into two groups, one that received low sulfur (0.19% S) and one that received high sulfur (0.39% S) through the addition of sodium sulfate into the ration. Each animal was fed their respective diet for 38 days and evaluated on days 0, 22, and 38 for ruminal hydrogen sulfide production. Ruminal fluid samples were also taken at these times to check for pH, ammonia nitrogen, volatile fatty acids, and microbes. The animals were also checked daily for any polioencephalomalacia symptoms.

Here is where things get interesting. Earlier, we talked about how the common hypothesis that dissimilatory sulfo-­reducing ruminal bacteria (DSRB) were the cause of increased hydrogen sulfide gas production. We would, in turn, expect to see increases in the quantity of DSRB to match that of hydrogen sulfide production. However, this was not the case. The high-sulfur group was indeed producing significantly more hydrogen sulfide, but there was no significant correlation between the gas levels and the DSRB population. Additionally, there were no significant effects of the sulfur treatment on the diversity of the tested rumen microbiome.

The lack of observed polioencephalomalacia occurrence, or any change in feed intake, suggests that the sulfur content of the high sulfur treatment was not enough to impact the animals. The authors point to the fact that the makeup of old and new diets (moving from forage-based to concentrate-based) could "...increase ruminal H2S [hydrogen sulfide] concentration more slowly, allowing animals to adapt to high dietary S [sulfur] concentration and/or H2S concentration." They continue, stating, " Hence, it is possible that for PEM [polioencephalomalacia] development, adaptation time to high ruminal H2S concentration is as important as high ruminal H2S concentration itself."

What makes this paper notable is not what the researchers found specifically, but what they didn't find. These researchers did not find that DSRB count was causing elevated hydrogen sulfide, but instead that the hypothesis was an incomplete one. These findings suggest there is much more at play in the rumen production of hydrogen sulfide than we initially thought, including the magnitude of the role of DSRB.

Important to note:

  • The low-sulfur diet had sulfur levels over the recommended concentrations. This was due to feedstuffs with high crude protein levels, which increased the total sulfur present. However, the concentrations were still much lower than the high-sulfur treatment.

Industry application: Although this paper didn't have an answer for avoiding sulfur toxicity or polioencephalomalacia, it offered some insightful information. When attempting to control sulfur toxicity in cattle, it is important to follow nutritional recommendations; however, this paper suggests that there may also be other factors at play, like ration transitions and diet composition.

Read more about it:

Ruminal effects of excessive dietary sulphur in feedlot cattle
Sulphur (S) dietary excess can limit productive performance and increase polioencephalomalacia (PEM) incidence in feedlot cattle (FC). Sulphur excess ingested is transformed to hydrogen sulphide (H2S...