Effect of unprotected methionine and choline on feed intake, growth, digestibility, fecal score, blood metabolites, and feeding behavior of suckling calves

Choline and methionine are crucial nutrients for livestock as they provide methyl groups. The relationship between these two nutrients is intricate, with varying opinions on their interdependence. Methionine is often a limiting amino acid in dairy diets and its metabolism is linked to that of choline and betaine. Choline as an alternative to methionine, can act as a precursor to phosphatidylcholine, which is important for dairy cows around calving time. Furthermore, choline and betaine impact methionine requirements and methionine can affect choline metabolism. Given that limited study and experimentation have been conducted so far to investigate the effects of unprotected methionine and choline on calves, this research aimed to examine the impact of unprotected methionine and choline on feed intake, growth, digestibility, fecal score, blood metabolites, and feed behavior of pre-weaned calves. The expected hypothesis of the study was the significant effect of utilizing unprotected methionine and choline on feed intake, growth, digestibility, fecal score, blood metabolites, and feeding behavior of pre-weaned calves due to their mono-gastric nature and lack of rumen development.

A total number of 32 Simmental male suckling calves, aged approximately one month old with an initial weight of 44±2.1 kg, were used in this study. The experimental treatments included: 1) a basal diet without choline and methionine (control), 2) the basal diet with three grams of methionine, 3) the basal diet with three grams of choline, and 4) the basal diet with 1.5 grams of methionine and 1.5 grams of choline per head per day. The calves were randomly assigned to the experimental treatments in a completely randomized design with eight replications. The study lasted for 45 days, including a 7-day adaptation period. Blood glucose, cholesterol, triglycerides, and urea nitrogen levels were measured on the last day of the study, four hours after morning feeding, to evaluate the metabolic profile of the animals. Additionally, feed consumption behavior was visually observed for 24 hours on the last day of the study to calculate the animal's rumination, eating, chewing, and resting time. To determine the digestibility of dry matter, samples were collected from feed and feces during the last three days of the experiment using the acid-insoluble ash internal indicator method. Stool consistency was scored for all of the calves as an indicator of animal health.

The inclusion of three grams of methionine in the experimental treatments resulted in a decrease in dry matter intake, and when methionine and choline were added, it increased the daily weight gain of the animals (P<0.05). However, the treatments did not have a significant effect on the feed conversion ratio (P>0.05). The results of other studies showed that the addition of choline did not have a significant effect on the amount of dry matter consumed, daily weight gain, and feed conversion ratio of Holstein bull calves. Consistent with the results of the present study, no improvement was observed in the feed efficiency of steers with the addition of a protected choline supplement, and no effect was observed on dry matter intake. The treatments did not have a significant impact on dry matter digestibility, stool consistency, blood glucose, cholesterol, triglyceride, and urea nitrogen (P>0.05). In agreement with the results of the present study, the digestibility of dry matter and organic matter in steers was not affected by choline. Researchers reported that the use of protected biocholine and methionine did not have a significant effect on the digestibility of dry matter in calves. Also, it was observed that the use of choline did not have a significant effect on the digestibility of dry matter in sheep and pre-weaned calves. Researchers have reported that the use of protected methionine and choline did not have a significant effect on the levels of glucose and triglycerides in the blood of dairy cows before calving. In another study, the urea nitrogen in the blood of dairy cows was not affected by methionine and choline. Additionally, the experimental treatments did not affect feed consumption behavior (P>0.05).

Feeding unprotected choline and methionine did not have a significant effect on glucose, cholesterol, triglycerides, blood urea nitrogen, digestibility of dry matter, fecal consistency score, and feeding behavior. However, the use of methionine improved dry matter intake and daily weight gain. Feeding Simmental calves with three grams of methionine per day is recommended to improve dry matter intake and daily weight gain, although it does not significantly affect the feed conversion ratio.