Production efficiency, milk yield, and milk composition and fatty acids profile of lactating goats feeding formaldehyde-treated canola meal in two levels of dietary crude protein

•Formaldehyde-treated canola meal increased milk and milk component yield.•Treated canola meal increased nutrients intake on high and low crude protein diets.•Formaldehyde treatment did not positively alter the fatty acids profile of milk.•Feeding formaldehyde-treated canola meal reduced ruminal NH3-N and plasma Urea-N. The effectiveness of formaldehyde treated canola meal (FTCM) in two levels of dietary crude protein (CP) were evaluated in an experiment. Eight multiparous lactating Raini goats (early lactation, 32 ± 2 kg BW) were used in a 4 × 4 Latin square design with four treatments. Experimental diets were: (1) diet with 14.5 % CP containing untreated canola meal (UCM) (CON), (2) diet with 14.5 % CP containing FTCM (0.8 g/100 g CP) (FT1), (3) diet with 14.5 % CP containing FTCM (1.2 g/100 g CP) (FT2), and (4) diet with 12.5 % CP containing FTCM (1.2 g/100 g CP) (LPFT2). Dry matter intake (DMI) of the goats was significantly increased by substitution of FTCM in the diet (P < 0.001). Feeding FT2 and LPFT2 diets significantly increased production of milk, fat-corrected milk (FCM), energy-corrected milk (ECM), total-solids-corrected milk (TSCM) (P < 0.001), and yields of fat, protein, lactose, total solids, and non-fat solids (P < 0.01). However, dietary treatments did not affect milk composition of the goats. Production efficiency for milk and FCM were highest (P < 0.001) in goats fed the LPFT2 diet. Moreover, the FT1 diet decreased C4:0, C6:0, C8:0, C10:0, C12:0, C15:0, C17:0, t-C18:3, and total short-chain and long-chain fatty acids (FA) of the milk (P ≤ 0.01), but C16:0 and total medium-chain FA were increased (P ≤ 0.01) as compared to CON and FT2. Although formaldehyde treating did not affect ruminal pH, the concentrations of ruminal ammonia-N (NH3-N), and blood urea-N (BUN) decreased by feeding FT2 and LPFT2 diets (P < 0.001). Also, LPFT2 diet increased concentration of total ruminal VFA (TVFA) and showed lower acetate/propionate ratio when fed to the goats (P < 0.05). In general, substitution of 1.2 % FTCM had improved feed intake and productive performance of lactating goats; it is therefore concluded that formaldehyde treating of canola meal can be used as an economical choice for increasing dietary bypass protein, by which the level of diet crude protein can be reduced.