Protein: How much of a good thing?

1. Nutrition

Protein: How much of a good thing?

Angora goat kids between weaning and 18 months are usually given additional nutritional support and often kept in small feeding lands or camps.

Farmers have observed that when feeding high protein feed, the kids seem not to do as well as those fed on a lower protein level. Is this a true observation? Can it be explained?

What is the role of protein in the diet?

The protein level in the diet can alter the gut microbes and affect the metabolites (essential amino acids) produced by gut bacteria. Enough dietary protein is essential for promoting growth and weight gain. 

Dietary protein provides amino acids involved in tissue synthesis, the immune system, and the metabolic system, all of which improve the production of ruminants.

How can a goat fed excess protein have a poorer growth rate and even undergo weight loss?

When a goat is fed a protein level higher than its body requires, energy removes excess protein instead of producing an increased average daily gain (ADG). The result can be a reduced rate of gain along with higher-than-necessary feed costs.

How does this happen?

Bacteria reduce protein to ammonia and then produce amino acids. Excess ammonia is absorbed through the wall of the rumen and circulates in the bloodstream. Ammonia can be toxic, so it must be converted from ammonia to urea. Urea is then excreted from the kidneys in the form of urine. A little excess protein can be tolerated. A high level of excess protein has both an energy cost in converting and excreting the excess ammonia as well as a monetary cost because protein is usually the most expensive nutrient in livestock feed.

What is the balance between too much protein and sufficient protein?

There is data on the maintenance protein requirements of goats available, but no study in Angora goats to pinpoint the ‘tipping point’ of excess protein that decreases production or where no additional benefit is gained at the extra cost.

This is also a difficult question to answer as we also need to consider the different phases of growth and production of the goat as well as the energy and mineral requirements. If we look at some studies done on various goat breeds and sheep, we may get an idea of the impact on some levels of dietary Protein.

Some trials reviewed the impact of Protein dietary levels on certain production parameters in sheep and goats.

From the literature (see below), it appears that Protein levels increase levels of production linearly to about 16-18%. Above this level, there may be no additional benefit and could result in poorer production. (Author’s interpretation). This is similar to Jan Hoon, a Nutrition researcher at Grootfontein, who suggests that protein levels around 15-16% would be optimum and 14-15% in the case of high-energy diets (11.7 & MJ energy). He also suggests maximum Protein levels around 17-18%.

• When diets of 10%, 12,5% and 15% protein levels were compared. The higher dietary protein levels increase milk production significantly. ¹
• Comparing CP levels of 11.5, 13.5, 15.5 and 17.5%. Milk production increased linearly with the increase of CP.²

• Trials on Saanen goats demonstrated a body weight loss (-0.03g/day) in diets of 19% CP.³ Dietary protein levels above 19% were not recommended because of the energy expenditure required to excrete the urea.
• The average daily gain of goats fed  14.0% and 16.0% CP diets was lower than that of goats fed the 18.0% CP diet.⁴
• There were no differences in the average daily gain of Barbari kids fed the 14.0% and 12.0% CP. ⁵ 
• 8, 10, 12 and 14% CP resulted in increased ADG with increased Protein levels.⁶
• Dietary CP protein levels of (i) 18% CP, (ii) 25.5% CP, (iii) 31.6% fed over a 4-month period to growing goats. Resulted in higher body condition scores on the higher Protein diet. ⁷
• Increasing protein levels: 7.5 %, 10.5 % and 14.5% resulted in (i) improved FAMACHA scores and (ii) increased growth performance in goats. ⁸
• Increasing dietary protein levels (8.38%, 10.42%, and 13.93%) in early lactating ewes increased daily gain and milk production. ⁹
• No benefit in ADG above 18% CP levels when fed up to 31% CP diet
• Protein appears to elicit more of an effect on mohair growth than wool growth. Increasing dietary protein above requirements increases mohair volume and fibre diameter.¹⁵

Impact of health status of high levels of protein. 

Communication with Scientists and Nutritionists within the industry, Dr Johan Van Rooyen and Jan Hoon, indicate that there can be a negative impact of high (excess) protein levels and mineral imbalances.

Little objective reference data is available. Some studies have shown no impact on different diet levels of protein supplementation on the health status of animals. Goats were fed protein 23.5% and given Lucerne ad lib.¹⁴ 

Studies showed that the blood urea nitrogen (BUN) in lactating ewes increased with increasing dietary protein levels. The increased BUN and ALB concentrations remained within normal ranges. An increase in urea in the urine of 2mg/dl was found for every 1% increase in CP in the diet above 19% ³

The highest urea (NPN) level observed did not pose any health hazard for the ewes. In studies where high levels of urea were used (4%), it did lead to lower body weight of lambs. The excess urea is excreted as ammonia via the kidneys, leading to an increase in urinary pH¹⁶. 

What are the maintenance Protein and Energy requirements of Angora goats?

For an explanation of the terms used in Protein discussions and the minimum Protein and Energy requirements of Angora goats at various stages of production, see the website ‘What is in a bag of feed?’ https://www.angoras.co.za/page/whats-in-a-bag-of-feed

Conclusion

Most diets are around 14-16% Protein and that in excess of 18% may be of no benefit (with additional costs). Very high levels may be detrimental.

It must be remembered that Energy, minerals, vitamins, and roughage need to be considered. Speak to your nutritionist for the best advice when formulating a ration for your goats.

See the article on the website ‘Lucerne - 2nd Grade better than 1st?’

REFERENCES

¹ Effects of Dietary Protein Level on Milk Production Performance and Serum Biochemical Indicators of Dairy Goat. Fansheng Meng, Cuilin Yuan and Ziyang Yu 

² Production of goats fed diets with increasing levels of protein: intake, milk yield and apparent digestibility. Carlos Elysio Moreira da Fonseca, Rilene Ferreira Diniz Valadares, Sebastião de Campos Valadares Filho, Marcelo Teixeira Rodrigues, Marcos Inácio Marcondes, Marlos Oliveira Porto, Douglas dos Santos Pina, Kamila Andreatta Kling de Moraes

³Crude protein levels in diets of lactating goats: nitrogen balance, urea excretion and microbial protein synthesis. Jesus dos Santos, Albuquerque Pereira, Pereira de Figueiredo, De Oliveira Silva, Ferreira Da Cruz, Oliveira Barreto, Borges Sousa

⁴ Effects of crude protein levels in total mixed rations on growth performance and meat quality in growing Korean Black goats. S Hwangbo, SH Choi, SW Kim, DS Son, HS Park, SH Lee, IH Jo

⁵ Effect of different protein-energy ratios in pulse by-product and residue-based pelleted feeds on growth, rumen fermentation, carcass and sausage quality in Barbari kids. TK Dutta, MK Agnihotri, PK Sahoo, V Rajkumar, AK Das

Reducing protein content in the diet of growing goats: implications for nitrogen balance, intestinal nutrient digestion and absorption, and rumen microbiota. X.X. Zhang, Y.X. Li, Z.R. Tang, W.Z. Sun, L.T. Wu, R. An, H.Y. Chen, K. Wan, Z.H. Sun 

⁶ Effects of dietary crude protein levels on nutrient digestibility and growth performance of Thai indigenous male goats. Jeerasak Chobtang, Intharak Kabuan, Isuwan Auraiwan

⁷ Effect of dietary protein level on growth and body condition score of male Beetal goats during summer. MohsinI, M. Q. ShahidI, M.N. HaqueII, N. Ahmadi, H. Mustafa 

⁸ Nutritional manipulation in goats: Supplementation of high protein concentrate affects the performance and resilience of internal parasites. Yusuf, A. O.,Ajayi, T. O.,Ajayi, O. S. and Yusuf, O. A

⁹ Vet. Sci., 03 August 2023. Animal Nutrition and Metabolism. Mpho Sylvia Tsheole, Mulunda Mwanza

¹⁰ Die effect van energiebyvoeding aan jong groeiende Angora bokkie. P D Grobbelaar en C M M Landman.

¹¹ Effect of energy level in Lucerne hay-based finishing diets on carcass characteristics of Dohne Merino lambs. V.N. Shivambu#, J.H. Hoon, W.J. Olivier & B.R. King

¹² Effect of level of supplementary feeding on Mohair production and reproductive performance of kraal-fed Angora ewes. P.R. King, V. Sumner, D. Wentzel, P. Schlebush and M.J. Herselman

¹³ Effect of Nutrition on certain Mohair Quality traits. Margaretha A Badenhorst, J C Diedericks & P A Schlebusch

¹⁴ Effect of different dietary protein levels on goats’ blood parameters of Tswana goats reared in extensive production systems 

¹⁵ Feeding and Nutrition. L. Rankins Jr, D.G. Pugh

¹⁶ Effect of different levels of urea supplementation on reproduction, production and physiological parameters of wool ewes. J.H. Hoon & J.A. van Rooyen

¹⁷ Nutritive Value of Four Lucerne Cultivars Planted in Two Soil Types at Bathurst Research Station, Mhlangabezi Solontsi, Mfundo Phakama Maqubela, Johan Adam van Niekerk, Jan Willem Swanepoel, Gideon Jordaan, Unathi Gulwa, Sive Tokozwayo

¹⁸ The nutritive value of South African Medicago sativa L. hay.G.D.J. ScholtzI, H.J. van der Merwe, T.P.     TylutkiII

²⁰ Cruywagen et al., 2011. S. Afr. J. Anim. Sci. vol. 4

²¹ Vough, L., 2001.  Evaluating hay quality. August 2008