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A meta-analysis to compare feed and milk N efficiency of Holstein and Jersey cows.

J. P. Sacramento

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06-23-2020

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Abstract:

T116
A meta-analysis to compare feed and milk N efficiency of Holstein and Jersey cows.
J. P. Sacramento*1,2, L. H. P. Silva1, D. C. Reyes1, L. G. R. Pereira3, A. F. Brito1. 1University of New Hampshire Durham, NH, 2Federal University of S�o Jo�o del Rei S�o Jo�o del Rei, MG, Brazil, 3Brazilian Agricultural Research Corporation EMBRAPA Dairy Cattle Juiz de Fora, MG, Brazil.

A meta-analysis was conducted to compare feed efficiency (FE) and milk N efficiency (MNE) between Holstein (HO) and Jersey (JE) cows. The data set was developed using the Web of Science database with the literature search ranging from 1980 to December 2019. The terms “Holstein,” “Jersey,” “milk yield,” and “milk production” were used in the Web of Science search engine to identify peer-reviewed articles yielding 166 hits. From this initial pool, 66 papers containing both breeds were selected with 12 articles retained in the final data set. The following criteria were adopted to include studies in the meta-analysis: (1) both purebred HO and JE used in the same trial; (2) DMI/breed or individual treatments; and (3) milk yield and composition. Feed efficiency was calculated as milk yield/DMI and ECM yield/DMI, while MNE was computed as milk N yield/N intake. Crude protein intake was estimated by multiplying DMI (kg/d) by the respective treatment CP concentration and converted to N intake (g/d). Milk N was computed by dividing milk protein by 6.38 for standardizing MNE. Breeds DIM averaged (mean � SD) 118 � 56, and mean BW for HO and JE was 616 � 55.4 and 437 � 56.2, respectively. Sixty-five observations (treatment means) were used in the meta-analysis, with 1 observation excluded from the data set as it was deemed outlier based on the −2.5 to 2.5 range of studentized residual. Data were analyzed using the MIXED procedure of SAS with the fixed effect of breed and the random effects of study and the breed by study interaction included in the statistical model. Holstein had greater DMI (20.9 vs. 17.2 kg/d; P < 0.001) and milk yield (31.2 vs. 22.3 kg/d; P < 0.001) than JE. Likewise, ECM yield was 16% greater in HO compared with JE (33.4 vs. 28.8 kg/d; P < 0.001). Holstein was also more efficient than JE to convert DMI into milk yield (1.51 vs 1.31; P < 0.001). However, when FE was calculated as ECM/DMI, JE had greater FE than HO (1.70 vs. 1.60; P = 0.03). In contrast, MNE did not differ significantly between breeds (mean = 29%). In brief, our meta-analysis revealed that HO and JE differ in FE but with similar MNE.

Keywords: efficiency, dairy cow, nitrogen.