Home loan growth at Westpac was muted over the month of April 2017, with the bank the only one of Australia's four major banks to report growth in mortgages below the banking system growth rate for mortgages of 0.45 per cent last month.Monthly banking statistics from APRA show growth in mortgages for Westpac over April of 0.33 per cent, around 0.7 times system.An obvious explanation is that Westpac has had to cut back harder recently than other banks on the supply of interest only loans. The bank did not respond to a request for comment yesterday.When reporting its half-year profit for the period to March 2017 earlier this month, Westpac put the interest-only component of the mortgage portfolio at 50 per cent and at 46 per cent of flows over six months.The bank will have to cut new flows of interest-only loans to 30 per cent by later this year or face grief from the banking regulator.Bendigo and Adelaide Bank also reported mortgage growth below system of 0.26 per cent.NAB and CBA slightly exceeded system growth while ANZ reported mortgage growth over the month of 0.57 per cent, close to 1.3 times system. NAB, CBA and ANZ thus appear unperturbed, at least in the short term, by APRA's recent macroprudential activism on interest-only loans.ANZ, in particular, has wound up, with its market share of 16.12 per cent (of all banks) 15 basis points greater than six months ago, in comparison with statis in the market share of CBA and NAB.Westpac's market share of 25.08 per cent is 18 bps lower than six months ago and 19 bps below its recent peak in market share of 25.27 per cent in November 2016.