Dietary supplement of the rumen protected methionine and milk yield in dairy goats

The experiment was conducted on three farms of dairy goats. The experimental groups of animals were during the four months period supplemented with 5g Mepron®, (Degussa, Germany), daily. Milk yield, milk protein and milk fat content were recorded throughout the experiment. The milk production was statistically higher in the experimental group of animals on two farms, farm 1 and farm 3 in the first control period, a month after the application, whereas on farm 2, the higher milk production was present in the third and forth control period, two and three months after the application. During the experiment there was no statistically differences in milk protein and milk fat content between experimental and control groups on farm 1 and farm 2, whereas on farm 3 the milk fat content was statistically lower during the Mepron® supplementation. In conclusion, the higher milk production in the first control period on farm 1 and 3 with great probability referred to the influence of Mepron®. The higher milk production on farm 2 in the third and fourth control period coincided with introduction of alfalfa hay in daily ration, that may have enriched the amino acid supply.


Introduction
Growing trend in consumption of goat milk and goat milk products initiate the modern dairy industry in order to improve the goat milk production and even to change the milk composition by dietary means.The immense amounts of research have been done on the dairy cow nutrition basis with a primary goal to higher milk production and eventually to manipulate milk protein and milk fat yield.The implement of the protected amino acids in dairy cows diet showed the improvements of the production of milk and milk proteins (OVERTON et al., 1996;PISULEWSKI and KOWALSKI, 1998).Although, the literature data are rather variable regarding the amino acid supplements and influence on the milk protein and milk fat synthesis in dairy cows it could be suspected the same effect on the dairy goats performance (OVERTON et al., 1996;OLIVEIRA et al., 2001;KIJORA et al., 2002;WANG et al., 2003).There were experimental model applied to show the gland amino acid uptake and partitioning in dairy goat and possible repercussion on the milk protein synthesis (LEE et al., 1999).The study on dairy goats of BAČAR-HUSKIĆ (1998) showed no significant changes in production of milk components but milk production elevated during the methionine supplementation.The aim of this work was to evaluate the effect of rumen protected methionine on the milk production, fat and protein content in milk of Alpine dairy goats at three different managed farms.

Material and Methods
Three farms were included in research with a total of 58 Alpine dairy goats.The average milk production and breeding performance of dairy goats are described in Table 1.The experiment was carried out during the four months and started at the beginning of lactation period, from April to July.The animals were on each farm randomly divided in two groups, the control and the experimental group.On two farms (farm 1 and farm 3) both group of animals were in the fourth to seventh lactation, and on farm 2, all animals were at the second lactation.The feeding procedure and applied technology was substantially the same at all farms, but differ in concentrate compo-

Results and Discussion
The experimental group of animals (MEP) showed statistically higher milk production (p ≤ 0,001) and (p ≤ 0,01) respectively, on two farms (farm 1 and farm 3), at first control period (Fig. 1. and Fig. 3.).On the other hand, milk production for MEP group of animals in all other control periods was near the level of CTRL group of animals.The milk production of MEP group on farm 2 was during the first and second control period near control level, whereas in the third and fourth control period milk production was statistically higher (p ≤ 0,01 and p ≤ 0,05 respectively), than in control group (Fig. 2.).During the whole experiment there were no statistically differences in protein and fat content between experimental and control milk samples on farm 1 and farm 2, whereas on farm three the MEP group had statistically lower fat content in milk.According to HAENLEIN (2001), fat and protein percentage measured on the machine calibrated with cow milk standards might have been underestimated by 0,04 and 0,27%, respectively.The lower milk fat content of MEP group of animals on farm 3 might have been related to basal diet in which soybean meal was incorporated in the concentrate mixture.The influence of active fats on the rumen biohydrogenation processes were discussed by many authors (BESSA et al., 2000;CHILLIARD et al., 2001;WALISIEWICZ-NIEDBLASKA et al., 2004).The presented results indicate that the supplementation of the protected methionine (Mepron®, Degussa) resulted in the higher milk production, whereas the milk components, total milk protein and milk fat content were mostly unaffected by this treatment.The results are in agreement with that of previous experiment conducted on Alpine goats (BAČAR-HUSKIĆ et al., 1998).The higher milk production in experimental group of animals was recorded on the different farms at the different stage of lactation.The reason for that incompatibility could be discussed in the light of concentrate composition that may have mayor roll in expression of supplemented rumen protected methionine.KIJORA et al. (2002) in their research stated strong relationship between feed intake and protein content in the ration of dairy goats, thus aminoacid protection might have provided also higher RDP level in duodenum of dairy goats in our research.In addition, parity and live weight of animals could have had the impact on the production results.The milk production on farm 2 reached the highest level at the third and forth month of experiment.The reason for postponed reaction we may attribute to age and parity (younger animals in second lactation).Moreover, the higher milk yield coincidences with the adding alfalfa hay in daily ration.On the other hand, in farm 1. and farm 3. the milk production in experimental group of animals increased between 6 and 9 week of lactation, what can with the great probability be considered as the influence of Mepron®.This conclusion is additionally supported by the fact that the goats from control groups reached this production value not until the week 10.At the time the animals were moved to more advanced pasture and also this period is known to be physiological peak of lactation curve in the goats.Beside that, the results of blood analysis, (unpublished data), indicated the variation of urea and mineral concentration, calcium and phosphorus between control and experimental group of animals which should be taken into account while forming the daily ration and using the supplemental feeding in dairy goats.
In conclusion, supplemental feeding with rumen protected methionine Mepron® influenced the production level of dairy goats and the intensity of response might have been also affected by the stage of lactation and diet composition.Positive effect on the milk yield is directly related to well-established lactation and nutritional quality.However, Mepron® had no influence on the total protein and fat content in milk, yet potential changes in protein fractions and composition are more feasible and should be considered in further trials.The regular control of blood metabolite and minerals during the supplemental feeding is needed since the higher production could change the mineral status, but also an antioxidative status of animals.

Table 2 Ingredients
, forage introduction and quality of management.Daily ration consisted of hay, concentrate, pasture, (May until July) or alfalfa hay on one farm only (Tab.2.).The experimental group was supplemented with 5g rumen protected aminoacid methionine (Mepron®, Degussa, Germany) per goat.Milk yield was recorded weekly and milk samples were collected every four week.The milk components were determined using automatic analyser «Milcoscan 605» (A.S.N.Foss Eletronic).The results were statistically evaluated with ANOVA (STATISTICA 6, Stat soft, USA, 2004).

Table 3
Milk components in control (CTRL) and experimental (MEP) group of dairy goats in the study (Milchbestandteile in der Kontrollgruppe (CTRL) und der Untersuchungsgruppe (MEP))