Anionic salts impose a metabolic acidosis which improve calcium homeostasis. Monitoring urine pH (UpH) is key to establishing effective use of anionic diets in prepartum cows. UpH ??between 6.0 and 7.0 can reduce hypocalcemia, however, it has often been suggested lowering the pH <6.0 for even better control of hypocalcemia. The pH is a log scale of the [H⁺]. Reducing the UpH from 8.5 to ??~5.5 indicates increasing proton excretion by the kidney of about 1000 fold. The objective was to establish the association between UpH of prepartum cows fed anionic diets and the incidence of postpartum disorders. The study was conducted between Jul 2018 and Jan 2019 in a herd from Argentina. Prepartum diet had a potential DCAD of – 90 mEq/kg DM. UpH of 200 prepartum cows were evaluated. UpH was categorized as <6.0 (n = 22); between 6.0 and 6.9 (n = 46); ≥ 7.0 (n = 135). The frequency in each UpH category for stillborn, dystocia, RFM, metritis, ketosis, LDA and mastitis was calculated. Logistic regression models were carried out for each disorder, considering as the main effect the UpH category, adjusting for days from pH evaluation to calving, parity, sex of the calf, type of parturition, season of urine pH evaluation, and BCS at calving. Models for all diseases, except stillborn, showed that the UpH was not associated with the incidence of the disorder. Cows with UpH <6.0 were 2.39 times more likely to have a stillborn than cows with UpH ≥6.0. These findings reinforce the importance of not lowering the urine pH to <6 in prepartum cows fed anionic salts. The marginal gain in the reduction of milk fever by lowering the pH to <6.0 is minimal, compared with an increase in the incidence of stillborn. Table 1 (Abstr. 217).

Urine pH	Stillbirth	Milk fever	Dystocia	RFM	Metritis	Ketosis	LDA	Mastitis
<6.0 (n=22)	13.6ª (3)	0.0 (0)	18.2 (4)	4.6 (1)	13.6 (3)	27.3 (6)	0.0 (0)	22.7 (5)
6.0-6.9 (n=46)	8.7b (4)	4.2 (2)	10.9 (5)	2.2 (1)	13.0 (6)	26.1 (12)	4.3 (2)	23.9 (11)
≥7.0 (n=135)	4.4b (6)	2.3 (3)	20.7 (28)	8.1 (11)	14.0 (19)	23.0 (31)	3.0 (4)	14.8 (20)
Comparison urine pH
<6.0 vs. ≥6.0	2.39	0.68	0.89	0.65	1.05	1.16	1.55	1.09
AOR (95% CI)	1.06-5.40	0.15-3.17	0.49-1.63	0.34-1.27	0.58-1.92	0.71-1.89	0.68-3.52	0.67-1.74
P-value	0.035	0.62	0.72	0.21	0.86	0.53	0.29	0.73